Iron filings in a magnetic field generated by a bar magnet

A magnet is a material or object that produces a magnetic field. A "hard" or "permanent" magnet is one which stays magnetized for a long time, such as magnets often used on refrigerator doors. Permanent magnets occur naturally in some rocks, particularly lodestone, but are now more commonly manufactured. A "soft" or "impermanent" magnet is one which loses its memory of previous magnetizations. "Soft" magnetic materials are often used in electromagnets to enhance (often hundreds or thousands of times) the magnetic field of a wire that carries an electrical current and is wrapped around the magnet; the field of the "soft" magnet increases with the current. Magnet can refer to: A magnet, an object that has a magnetic field Magnet, a commune in the Allier département, in France Magnet, Nebraska, a town in the United States Magnet school Magnet link, an URI often used in conjunction with Peer-to-peer networks. ... Image File history File links Magnet0873. ... Image File history File links Magnet0873. ... Magnetic field lines shown by iron filings Magnetostatics Electrodynamics Electrical Network Tensors in Relativity This box:      In physics, the magnetic field is a field that permeates space and which exerts a magnetic force on moving electric charges and magnetic dipoles. ... Rock redirects here. ... Magnetite Lodestone or loadstone refers to either: Magnetite, a magnetic mineral form of iron(II), iron(III) oxide Fe3O4, one of several iron oxides. ... An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. ... In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ...

Two measures of a material's magnetic properties are its magnetic moment and its magnetization. A material without a permanent magnetic moment can, in the presence of magnetic fields, be attracted (paramagnetic), or repelled (diamagnetic). Liquid oxygen is paramagnetic; graphite is diamagnetic. Paramagnets tend to intensify the magnetic field in their vicinity, whereas diamagnets tend to weaken it. "Soft" magnets, which are strongly attracted to magnetic fields, can be thought of as strongly paramagnetic; superconductors, which are strongly repelled by magnetic fields, can be thought of as strongly diamagnetic. Paramagnetism is the tendency of the atomic magnetic dipoles, due to quantum-mechanical spin, in a material that is otherwise non-magnetic to align with an external magnetic field. ... Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... For other uses, see Graphite (disambiguation). ... Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. ...

Qualities

The magnetic field, magnetic moment, and magnetization are vectors, meaning they have direction and magnitude. The magnetic moment and magnetization are properties only of the magnet, while the magnetic field it produces depends on the position relative to the magnet. The magnetic moment points from its south pole to its north pole. Also, its north pole points towards the Earth's geographic north pole, which is a magnetic south pole. A compass needle is approximately a bar magnet. This article is about vectors that have a particular relation to the spatial coordinates. ...

Magnetic field strength

The effects of magnetism.

A magnetic field can be measured using a good magnetic compass (this is a small permanent magnet). The direction of the field at a point in space is the direction in which the compass needle points when it passes through that point and is in equilibrium. The magnitude (or strength, usually denoted by the symbol B) of a magnetic field can also be measured using a compass, if the field is, like the Earth's, nearly uniform over the volume occupied by the needle. The needle is rotated about its center, and this makes it oscillate about its equilibrium position. The period t of oscillation is measured. For small oscillation angles, the frequency of the oscillation, 1/t, is proportional to the square root of B. This is a result from the theory of rotational motion and the theory of the torque on a magnet, and can be tested by creating an electromagnet, which makes a magnetic field proportional to the electric current that it carries. The common unit of magnetic field is the tesla, denoted "T", equal to one N/(A·m) (Force/(Current·Distance)), or Wb/m² (magnetic flux per area), and about 20,000 times the Earth's magnetic field. Technically, B should be called the magnetic induction field, because changing B induces an electric field, by Faraday's Law of electromagnetic induction. Image File history File links Metadata Size of this preview: 450 × 600 pixelsFull resolution (1704 × 2272 pixel, file size: 515 KB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Metadata Size of this preview: 450 × 600 pixelsFull resolution (1704 × 2272 pixel, file size: 515 KB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... This article is about the navigational instrument. ... This article is about Earth as a planet. ... For other uses, see Frequency (disambiguation). ... The word proportionality may have one of a number of meanings: In mathematics, proportionality is a mathematical relation between two quantities. ... Tesla may refer to: In science: Nikola Tesla, a Serbian-American physicist, inventor, and electrical engineer List of Tesla patents IEEE Nikola Tesla Award, an annual award given by the Institute of Electrical and Electronics Engineers (IEEE) Nikola Tesla Museum, Belgrade, Serbia Nikola Tesla elementary school, Novi Sad, Serbia Nikola... In physics, the weber (symbol: Wb) is the SI unit of magnetic flux. ... Magnetic flux, represented by the Greek letter Φ (phi), is a measure of quantity of magnetism, taking account of the strength and the extent of a magnetic field. ... The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... Faradays law can mean: Faradays law of induction (electromagnetic fields) Faradays law of electrolysis Category: ...

Magnetic moment

The magnetic moment μ of a magnet is the magnetic strength of the field at a distance r from the magnet. At large distances, the magnetic field B is proportional to μ and inversely proportional to r³. So, μ can be obtained by measuring B at a distance r. The common unit for magnetic moment is A·m². A wire in the shape of a circle with area A and carrying current I has a magnetic moment equal to IA.

Magnetization

Magnetization of an object is its magnetic moment per unit volume. It is usually denoted M and has the units A/m. A good bar magnet may have a magnetic moment of 0.1 A·m² and a volume of 1 cm³, or 0.000001 m³, and therefore a magnetization of 100,000 A/m. Iron can have a magnetization of around a million A/m.

Magnetic Domains

Magnetic domains in ferromagnetic material.

The magnetic moment of atoms in a ferromagnetic material cause them to behave something like tiny permanent magnets. They stick together and align themselves into small regions of more or less uniform alignment called magnetic domains or Weiss domains. Magnetic domains can be observed with Magnetic force microscope to reveal magnetic domain boundaries that resemble white lines in the sketch.There are many scientific experiments that can physically show magnetic fields. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Ferromagnetism is the phenomenon by which materials, such as iron, in an external magnetic field become magnetized and remain magnetized for a period after the material is no longer in the field. ... This article or section is in need of attention from an expert on the subject. ... Charge seperation between the positive and negative ions is the reason for electric dipole behavior. ... A magnetic force microscope (MFM) is a scanning probe microscope (SPM) that can map the spatial distribution of magnetism by measuring the magnetic interaction between a sample and a tip. ...

Effect of a magnet on the domains.

When a domain contains too many molecules, it becomes unstable and divides into two domains aligned in opposite directions so that they stick together more stably as shown at the right. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

When exposed to a magnetic field, the domain boundaries move so that the domains aligned with the magnetic field grow and dominate the structure as shown at the left. When the magnetizing field is removed, the domains may not return to a unmagnetized state. This results in the ferromagnetic material being magnetized, forming a permanent magnet.

When magnetized strongly enough that the prevailing domain overruns all others to result in only one single domain, the material is magnetically saturated. When a magnetized ferromagnetic material is heated to the Curie point temperature, the molecules are agitated to the point that the magnetic domains lose the organization and the magnetic properties they cause cease. When the material is cooled, this domain alignment structure spontaneously returns as the material develops its crystalline structure. The Curie point is a term in physics and materials science, named after Pierre Curie (1859-1906), and refers to a characteristic property of a ferromagnetic material. ...

Physical origin of magnetism

Magnetism, ultimately, is due to the motion of electric charge. For a macroscopic object, like a wire loop, an electric current flowing through it has a magnetic moment. Far from the loop there is a magnetic field proportional in strength to its magnetic moment.

For a microscopic object, the physical picture is more complex. An electron within an atom can have orbital angular momentum and a magnetic moment proportional to that orbital angular momentum; the electron also has intrinsic angular momentum, or spin, and a magnetic moment proportional to that spin angular momentum. The orbital and spin angular momentum of an electron are comparable in magnitude, as are their magnetic moments. Far from the electron there is a magnetic field proportional in strength to its magnetic moment.

In addition, within the atomic nucleus are both neutrons and protons, and these too have orbital and spin angular momentum, and associated magnetic moments. However, the nuclear magnetic moment typically is much smaller than the electron magnetic moment, because although the magnetic moment is proportional to its angular momentum (comparable to that of the electron) it is also inversely proportional to its mass. Nevertheless, it is the nucleus's relatively small nuclear magnetic moment that is responsible for nuclear magnetic resonance (NMR), which is the basis for magnetic resonance imaging (MRI). NMR redirects here. ... “MRI” redirects here. ...

Although most atoms and molecules have a net magnetic moment at temperatures well below room temperature, at room temperature they typically have no net magnetic moment. However, they can often be magnetized. If the orbital magnetic properties dominate, the response typically will be diamagnetic; if the intrinsic magnetic properties dominate, the response typically will be paramagnetic.

Solids are collections of atoms and molecules. At room temperature most solids are either diamagnetic or paramagnetic. Properties For alternative meanings see atom (disambiguation). ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. ...

Although for many purposes it is convenient to think of a magnet as having magnetic poles, it must be remembered that no isolated magnetic pole has ever been observed. As indicated above, the proper description is ultimately one due to electrical currents. For a magnet, these currents should be thought of as circulating about its atoms, and flowing without any electrical resistance. This physical picture is due to André-Marie Ampère, and these atomic currents are known as Amperian currents. For a uniformly magnetized bar magnet in the shape of a cylinder, the net effect of the atomic currents is to make the magnet behave as if there is a sheet of current flowing around the cylinder, with local flow direction normal to the cylinder axis. A right-hand-rule due to Ampère tells us how the currents flow, for a given magnetic moment. Align the thumb of your right hand along the magnetic moment, and with that hand grasp the cylinder. Your fingers will then point along the direction of current flow. André-Marie Ampère (January 20, 1775 – June 10, 1836), was a French physicist who is generally credited as one of the main discoverers of electromagnetism. ...

Permanent magnets

A few elements -- especially iron, cobalt, and nickel -- are ferromagnetic at room temperature. When quantum mechanics and the Pauli Exclusion Principle are accounted for, the electrical energy within these atoms is found to be lower if the magnetic moments of the valence electrons are aligned. This makes them ferromagnetic. Every ferromagnet has its own individual temperature, called the Curie temperature, or Curie point, above which it loses its ferromagnetic properties. This is because the thermal tendency to disorder overwhelms the energy lowering due to ferromagnetic order. A perfectly aligned ferromagnet is said to have long-range order because all of its atoms have their magnetic moments pointing in the same direction. Real ferromagnets are not perfectly aligned, but rather contain perfectly aligned regions, called magnetic domains, which have their own magnetization directions. Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... For a less technical and generally accessible introduction to the topic, see Introduction to quantum mechanics. ... The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925. ... A bar magnet. ... In chemistry, valence electrons are the electrons contained in the outermost, or valence, electron shell of an atom. ... In physics, the Curie point, or Curie temperature, is the temperature above which a ferromagnet loses its ferromagnetic ability to possess a net (spontaneous) magnetization in the absence of an external magnetic field. ... This article or section is in need of attention from an expert on the subject. ...

A long bar magnet appears to have a north pole at one end and a south pole at the other. Near either end the magnetic field falls off inversely with the square of the distance from that pole.

For a magnet of any shape, at distances large compared to its size, the strength of the magnetic field falls off inversely with the cube of the distance from the magnet's center.

Electromagnets

Main article: electromagnet

An electromagnet in its simplest form, is a wire that has been coiled into one or more loops, known as a solenoid. When electric current flows through the wire, a magnetic field is generated. It is concentrated near the coil, and its field lines are very similar to those for a magnet. The orientation of this effective magnet is determined via the right hand rule. The magnetic moment and the magnetic field of the electromagnet are proportional to the number of loops of wire, to the cross-section of each loop, and to the current passing through the wire. An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. ... For other uses, see Solenoid (disambiguation). ... The right hand rule is also an algorithm used to solve Mazes In mathematics and physics, the right-hand rule is a convention for determining relative directions of certain vectors. ...

If the coil of wire is wrapped around a material with no special magnetic properties (i.e., cardboard), it will tend to generate a very weak field. However, if it is wrapped around a "soft" ferromagnetic material, such as an iron nail, then the net field produced can result in a several hundred- to thousandfold increase of field strength. Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ...

Uses for electromagnets include particle accelerators, electric motors, junkyard cranes, and magnetic resonance imaging machines. Some applications involve configurations more than a simple magnetic dipole; for example, quadrupole magnets are used to focus particle beams. For the DC Comics Superhero also called Atom Smasher, see Albert Rothstein. ... “MRI” redirects here. ... Quadrapole magnets sometimes called correctors, are designed to create a magnetic field whose magnitude grows linearly with the radial distance from its longitudinal axis, which is usually centered on and parallel to the main motion of the charged particles. ...

Characteristics

Permanent magnets and dipoles

All magnets appear to have at least one north pole (reckoned positive) and at least one south pole (reckoned negative), and the net pole strength of every magnet is zero. Despite their apparent reality, as suggested by the image at the top of the page, where iron filings concentrate in regions of large magnetic field, poles are not physical objects on or in the magnet. They are simply a useful concept for describing magnets. Rather than poles being the fundamental unit, it is the magnetic dipole that is the fundamental unit. A magnetic dipole can be thought of as a combination of a positive and a negative pole that are microscopically close to one another and inseparable. This is not a bad description of the magnetic dipole of an electron in a magnetic material.

The effect of aligning many dipoles and placing them head-to-tail in a line is that there appears a north pole at one end and a south pole at the other, with all the intermediate north and south poles canceling out. The net effect is a very long dipole that appears to have poles only at its ends. Alternatively, aligning many dipoles and placing them on a sheet produces an object whose magnetic field is like that of a wire carrying current around the perimeter of the sheet.

North-south pole designation and the Earth's magnetic field

See also: Earth's magnetic field, North Pole, South Pole, and Magnetic North Pole

A standard naming system for the poles of magnets is important. Historically, the terms north and south reflect awareness of the relationship between magnets and the earth's magnetic field. A freely suspended magnet will eventually orient itself north-to-south, because of its attraction to the north and south magnetic poles of the earth. The end of a magnet that points (approximately) toward the Earth's geographic North Pole is labeled as the north pole of the magnet; correspondingly, the end that points south is the south pole of the magnet. (The actual geographic north pole is in a slightly different location than the corresponding magnetic pole; see Magnetic North Pole.) The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... For other uses, see North Pole (disambiguation). ... For other uses, see South Pole (disambiguation). ... This is about the geographic meaning of North Pole. ... The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... This article is about Earth as a planet. ... For other uses, see North Pole (disambiguation). ... This is about the geographic meaning of North Pole. ...

The Earth's present geographic north is thus actually its magnetic south. Confounding the situation further, magnetized rocks on the ocean floor show that the Earth's magnetic field has reversed itself in the past, so this system of naming is likely to be incorrect at some time in the future. Recent geomagnetic reversals. ...

Fortunately, by using an electromagnet and the right hand rule relating the electromagnet's current and the magnetic field it produces, the orientation of the field of a magnet can be defined without reference to the Earth's geomagnetic field. The right hand rule is also an algorithm used to solve Mazes In mathematics and physics, the right-hand rule is a convention for determining relative directions of certain vectors. ...

To avoid the confusion between geographic and magnetic north and south poles, the terms positive and negative are sometimes used for the poles of a magnet. The positive pole is that which seeks geographical north.

Common uses

Magnets have many uses in toys. M-tic uses magnetic rods connected to metal spheres for construction

• Magnetic recording media: Common VHS tapes contain a reel of magnetic tape. The information that makes up the video and sound is encoded on the magnetic coating on the tape. Common audio cassettes also rely on magnetic tape. Similarly, in computers, floppy disks and hard disks record data on a thin magnetic coating.

• Credit, debit, and ATM cards: All of these cards have a magnetic strip on one of their sides. This strip contains the necessary information to contact an individual's financial institution and connect with their account(s).

• Common televisions and computer monitors: TV and computer screens using vacuum tube technology employ an electromagnet to guide electrons to the screen, in order to produce an image -- see the article on cathode ray tubes. Plasma screens and LCDs use different technologies.

• Speakers and microphones: Most speakers employ a permanent magnet and a current-carrying coil to convert electric energy (the signal) into mechanical energy (the sound). The coil is wrapped around the speaker cone, and carries the signal, producing a changing magnetic field that interacts with the field of the permanent magnet. The low mass coil feels a magnetic force and in response moves the cone and the neighboring air, thus generating sound. Standard microphones employ the same concept, but in reverse. A microphone has a cone or membrane attached to a coil of wire. The coil rests inside a specially shaped magnet. When sound vibrates the membrane, the coil is vibrated as well. As the coil moves through the magnetic field, a voltage is generated in the coil (see Lenz's Law). This voltage drives current in the wire that is characteristic of the original sound.

Magnetic hand separator for heavy minerals

• Electric motors and generators: Some electric motors (much like loudspeakers) rely upon a combination of an electromagnet and a permanent magnet, and much like loudspeakers, they convert electric energy into mechanical energy. A generator is the reverse: it converts mechanical energy into electric energy.

• Transformers: Transformers are devices that transfer electric energy between two windings that are electrically isolated but are linked magnetically.

• Chucks: Chucks are used in the metalworking field to hold objects. If these objects can be held securely with a magnet then a permanent or electromagnetic chuck may be used. Magnets are also used in other types of fastening devices, such as the magnetic base, the magnetic clamp and the refrigerator magnet.

• A compass (or mariner's compass) is a navigational instrument for finding directions on the Earth. It consists of a magnetized pointer free to align itself accurately with Earth's magnetic field, which is of great assistance in navigation. The cardinal points are north, south, east and west. A compass can be used in conjunction with a marine chronometer and a sextant to provide a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient. An early form of the compass was invented in China in the 11th century. The familiar mariner's compass was invented in Europe around 1300, as was later the liquid compass and the gyrocompass which does not work with a magnetic field.

• Magic: Naturally magnetic Lodestones as well as iron magnets are used in conjunction with fine iron grains (called "magnetic sand") in the practice of the African-American folk magic known as hoodoo. The stones are symbolically linked to people's names and ritually sprinkled with magnetic sand to reveal the magnetic field. One stone may be utilized to bring desired things to a person; a pair of stones may be manipulated to bring two people closer together in love.

• Art: 1 mm or thicker vinyl magnet sheets may be attached to paintings, photographs, and other ornamental articles, allowing them to be stuck to refrigerators and other metal surfaces.

• Science Projects: Many topic questions are often based on magnets. For example; how is the strength of a magnet affected by glass, plastic, and cardboard?

• Toys: Due to their ability to counteract the force of gravity at very close range, magnets are often employed in children's toys such as the Magnet Space Wheel to amusing effect.

• Magnets can be used to make jewelry. Necklaces and bracelets can have a magnetic clasp. Necklaces and bracelets can be made from small but strong, cylindrical magnets and slightly larger iron or steel balls connected in a pattern that is repeated until it is long enough to fit on the wrist or neck. These accessories may be fragile enough to accidentally come apart, but they also can be disassembled and reassembled with a different design. When connected as a necklace or a bracelet, magnets lose their attraction to other pieces of iron steel because they are already attached to their own iron and steel balls. Magnetic lip-rings and earrings are sometimes employed to avoid piercing.

• Magnets can pick up magnetic items (iron nails, staples, tacks, paper clips) that are either too small, too hard to reach, or too thin for fingers to hold.

• Magnetic levitation transport, or maglev, is a form of transportation that suspends, guides and propels vehicles (especially trains) via electromagnetic force. This method can be faster than wheeled mass transit systems, potentially reaching velocities comparable to turboprop and jet aircraft (900 km/h, 559 mph). The maximum recorded speed of a maglev train is 581 km/h (361 mph), achieved in Japan in 2003.

• A recently developed use of magnetism is to connect portable computer power cables. Such a connection will occasionally break by accidentally pushing against the cable, but the computer battery prevents interruption of service, and the easy disconnection protects the cable from serious jerks or from being stepped on.

Image File history File links Download high-resolution version (1033x995, 131 KB) M-tic - a magnetic construction toy File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Magnet ... Image File history File links Download high-resolution version (1033x995, 131 KB) M-tic - a magnetic construction toy File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Magnet ... Bottom view of VHS cassette with magnetic tape exposed Top view of VHS cassette with front casing removed The Video Home System, better known by its abbreviation VHS, is a recording and playing standard. ... Compact audio cassette Magnetic tape is a non-volatile storage medium consisting of a magnetic coating on a thin plastic strip. ... Typical 60-minute Compact Cassette. ... A floppy disk is a data storage device that is composed of a disk of thin, flexible (floppy) magnetic storage medium encased in a square or rectangular plastic shell. ... Typical hard drives of the mid-1990s. ... Look up credit card in Wiktionary, the free dictionary. ... Look up debit card in Wiktionary, the free dictionary. ... Outdoor ATMs may be free-standing, like this kiosk, or built into the side of banks or other buildings An automatic teller machine, automated teller machine (ATM) or cash machine is an electronic device that allows a banks customers to make cash withdrawals and check their account balances without... Nineteen inch (48 cm) CRT computer monitor A computer display, monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. ... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT: 1. ... A plasma display is an emissive flat panel display where light is created by phosphors excited by a plasma discharge between two flat panels of glass. ... LCD redirects here. ... For the Marty Friedman album, see Loudspeaker (album) An inexpensive low fidelity 3. ... Microphones redirects here. ... Lenzs law (pronounced (IPA) ) gives the direction of the induced electromotive force (emf) and current resulting from electromagnetic induction. ... Image File history File linksMetadata Download high-resolution version (1582x1358, 182 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Magnet Black sand Heavy mineral sands ore deposits Metadata This file contains additional information, probably added from the... Image File history File linksMetadata Download high-resolution version (1582x1358, 182 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Magnet Black sand Heavy mineral sands ore deposits Metadata This file contains additional information, probably added from the... For other kinds of motors, see motor. ... This article is about machines that produce electricity. ... For other uses, see Transformer (disambiguation). ... A Chuck is a specialised type of clamp used to hold rotating tools or materials. ... Turned chess pieces Metalworking is the craft and practice of working with metals to create structures or machine parts. ... A Chuck is a specialised type of clamp used to hold rotating tools or materials. ... Magnetic base as used in the engineering metaltrades. ... A refrigerator magnet (or fridge magnet) is a piece of ornament attached to a magnet that is used to decorate refrigerator doors. ... “Illusionist” redirects here. ... Magnetite Lodestone or loadstone refers to either: Magnetite, a magnetic mineral form of iron(II), iron(III) oxide Fe3O4, one of several iron oxides. ... Languages Predominantly American English Religions Protestantism (chiefly Baptist and Methodist); Roman Catholicism; Islam Related ethnic groups Sub-Saharan Africans and other African groups, some with Native American groups. ... This does not adequately cite its references or sources. ... This article is about the philosophical concept of Art. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... The Magnet Space Wheel is a toy that propels a plastic wheel along both sides of a metal track with magnets built into the wheel. ...

Magnetization and demagnetization

Ferromagnetic materials can be magnetized in the following ways: Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ...

• Placing the item in an external magnetic field will result in the item retaining some of the magnetism on removal. Vibration has been shown to increase the effect. Ferrous materials aligned with the earth's magnetic field and which are subject to vibration (e.g. frame of a conveyor) have been shown to acquire significant residual magnetism.
• Placing the item in a solenoid with a direct current passing through it.
• Stroking - An existing magnet is moved from one end of the item to the other repeatedly in the same direction.
• Placing a steel bar in a magnetic field, then heating it to a high temperature and then finally hammering it as it cools. This can be done by laying the magnet in a North-South direction in the Earth's magnetic field. In this case, the magnet is not very strong but the effect is permanent.

Permanent magnets can be demagnetized in the following ways: Oscillation is the variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. ... For other uses, see Solenoid (disambiguation). ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...

• Heating a magnet past its Curie point will destroy the long range ordering.
• Contact through stroking one magnet with another in random fashion will demagnetize the magnet being stroked, in some cases; some materials have a very high coercive field and cannot be demagnetized with other permanent magnets.
• Hammering or jarring will destroy the long range ordering within the magnet.
• A magnet being placed in a solenoid which has an alternating current being passed through it will have its long range ordering disrupted, in much the same way that direct current can cause ordering.

In an electromagnet which uses a soft iron core, ceasing the flow of current will eliminate the magnetic field. However, a slight field may remain in the core material as a result of hysteresis. For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... The Curie point is a term in physics and materials science, named after Pierre Curie (1859-1906), and refers to a characteristic property of a ferromagnetic material. ... For other uses, see Solenoid (disambiguation). ... City lights viewed in a motion blurred exposure. ... A system with hysteresis exhibits path-dependence, or rate-independent memory. Consider a deterministic system with no hysteresis and no dynamics. ...

Types of permanent magnets

A stack of ferrite magnets

Image File history File linksMetadata Download high resolution version (1496x1378, 260 KB) A stack of ceramic/ferrite magnets with some various metal objects. ... Image File history File linksMetadata Download high resolution version (1496x1378, 260 KB) A stack of ceramic/ferrite magnets with some various metal objects. ...

Magnetic metallic elements

Many materials have unpaired electron spins, and the majority of these materials are paramagnetic. When the spins interact with each other in such a way that the spins align spontaneously, the materials are called ferromagnetic (what is often loosely termed as "magnetic"). Due to the way their regular crystalline atomic structure causes their spins to interact, some metals are (ferro)magnetic when found in their natural states, as ores. These include iron ore (magnetite or lodestone), cobalt and nickel, as well the rare earth metals gadolinium and dysprosium (when at a very low temperature). Such naturally occurring (ferro)magnets were used in the first experiments with magnetism. Technology has since expanded the availability of magnetic materials to include various manmade products, all based, however, on naturally magnetic elements. Paramagnetism is the tendency of the atomic magnetic dipoles, due to quantum-mechanical spin, in a material that is otherwise non-magnetic to align with an external magnetic field. ... Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... Crystal (disambiguation) Insulin crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... Properties For alternative meanings see atom (disambiguation). ... This article is about metallic materials. ... For other uses, see Ore (disambiguation). ... This heap of iron ore pellets will be used in steel production. ... Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ... Magnetite Lodestone or loadstone refers to either: Magnetite, a magnetic mineral form of iron(II), iron(III) oxide Fe3O4, one of several iron oxides. ... For other uses, see Cobalt (disambiguation). ... For other uses, see Nickel (disambiguation). ... General Name, Symbol, Number gadolinium, Gd, 64 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 157. ... General Name, Symbol, Number dysprosium, Dy, 66 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 162. ...

Composites

Ceramic or ferrite

Ceramic, or ferrite, magnets are made of a sintered composite of powdered iron oxide and barium/strontium carbonate ceramic. Due to the low cost of the materials and manufacturing methods, inexpensive magnets (or nonmagnetized ferromagnetic cores, for use in electronic component such as radio antennas, for example) of various shapes can be easily mass produced. The resulting magnets are noncorroding, but brittle and must be treated like other ceramics. Sintering is a method for making objects from powder, increasing the adhesion between particles as they are heated. ... A cloth of woven carbon fiber filaments, a common element in composite materials Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure. ... This article is about ceramic materials. ... Various components An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads. ... A Yagi-Uda beam antenna Short Wave Curtain Antenna (Moosbrunn, Austria) An antenna or aerial is an arrangement of aerial electrical conductors designed to transmit or receive radio waves which is a class of electromagnetic waves. ... A material is brittle if it is subject to fracture when subjected to stress i. ...

Alnico

Alnico magnets are made by casting or sintering a combination of aluminium, nickel and cobalt with iron and small amounts of other elements added to enhance the properties of the magnet. Sintering offers superior mechanical characteristics, whereas casting delivers higher magnetic fields and allows for the design of intricate shapes. Alnico magnets resist corrosion and have physical properties more forgiving than ferrite, but not quite as desirable as a metal. This article is about the manufacturing process. ... This article or section does not cite its references or sources. ... Aluminum redirects here. ...

Injection molded

Injection molded magnets are a composite of various types of resin and magnetic powders, allowing parts of complex shapes to be manufactured by injection molding. The physical and magnetic properties of the product depend on the raw materials, but are generally lower in magnetic strength and resemble plastics in their physical properties. Injection molding is a manufacturing technique for making parts from thermoplastic material in production. ... Look up composite in Wiktionary, the free dictionary. ... This article does not cite any references or sources. ... For other uses, see Plastic (disambiguation). ...

Flexible

Flexible magnets are similar to injection molded magnets, using a flexible resin or binder such as vinyl, and produced in flat strips or sheets. These magnets are lower in magnetic strength but can be very flexible, depending on the binder used. Chemical structure of the vinyl functional group. ...

Rare earth magnets

Main article: Rare-earth magnet

'Rare earth' (lanthanoid) elements have a partially occupied f electron shell (which can accommodate up to 14 electrons.) The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore these elements are used in compact high-strength magnets where their higher price is not a concern. Ferrofluid on glass, with a rare-earth magnet underneath. ... The lanthanide series comprises the 15 rare earth elements from lanthanum to lutetium on the periodic table, with atomic numbers 57 through 71. ... Example of a sodium electron shell model An electron shell, also known as a main energy level, is a group of atomic orbitals with the same value of the principal quantum number n. ...

Samarium-cobalt

Samarium-cobalt magnets are highly resistant to oxidation, with higher magnetic strength and temperature resistance than alnico or ceramic materials. Sintered samarium-cobalt magnets are brittle and prone to chipping and cracking and may fracture when subjected to thermal shock. Samarium-cobalt magnets (SmCo5) are composed of samarium and cobalt. ...

Neodymium-iron-boron (NIB)

Neodymium magnets, more formally referred to as neodymium-iron-boron (NdFeB) magnets, have the highest magnetic field strength, but are inferior to samarium cobalt in resistance to oxidation and temperature. This type of magnet has traditionally been expensive, due to both the cost of raw materials and licensing of the patents involved. This high cost limited their use to applications where such high strengths from a compact magnet are critical. Use of protective surface treatments such as gold, nickel, zinc and tin plating and epoxy resin coating can provide corrosion protection where required. Beginning in the 1980s, NIB magnets have increasingly become less expensive and more popular in other applications such as children's magnetic building toys. Even tiny neodymium magnets are very powerful and have important safety considerations.^[1] Neodymium magnet on a bracket from a hard drive A neodymium magnet or NIB magnet (also, but less specifically, called a rare-earth magnet) is a powerful magnet made of a combination of neodymium, iron, and boron — Nd2Fe14B. They have replaced marginally weaker and significantly more heat-resistant samarium-cobalt... For the hazard, see corrosive. ... Look up nib in Wiktionary, the free dictionary. ...

Single-molecule magnets (SMMs) and single-chain magnets (SCMs)

In the 1990s it was discovered that certain molecules containing paramagnetic metal ions are capable of storing a magnetic moment at very low temperatures. These are very different from conventional magnets that store information at a "domain" level and theoretically could provide a far denser storage medium than conventional magnets. In this direction research on monolayers of SMMs is currently under way. Very briefly, the two main attributes of an SMM are:

1. a large ground state spin value (S), which is provided by ferromagnetic or ferrimagnetic coupling between the paramagnetic metal centres.
2. a negative value of the anisotropy of the zero field splitting (D)

Most SMM's contain manganese, but can also be found with vanadium, iron, nickel and cobalt clusters. More recently it has been found that some chain systems can also display a magnetization which persists for long times at relatively higher temperatures. These systems have been called single-chain magnets. Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... A ferrimagnetic interaction is a specific type of antiferromagnetic interaction in which the net spin of the system is not equal to zero due to the spin in each direction not being equal, and therefore not cancelling. ...

Nano-structured magnets

Some nano-structured materials exhibit energy waves called magnons that coalesce into a common ground state in the manner of a Bose-Einstein condensate. Surface waves in water This article is about waves in the most general scientific sense. ... There is a place named Magnon (pronunciation: ma-nyon) in Gabon, see Magnon, Gabon A magnon is a collective excitation of the electrons spin structure in a crystal lattice. ... A Bose–Einstein condensate is a phase of matter formed by bosons cooled to temperatures very near to absolute zero (0 kelvins or -273. ...

See results from NIST published April 2005,^[2] or^[3] As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ...

Magnetic behaviors

Please help improve this article or section by expanding it. Further information might be found on the talk page or at requests for expansion. (March 2007)

There are many forms of magnetic behavior, and all materials exhibit at least one of these behaviors. Magnets vary in the permanency of their magnetization and the strength of the magnetic field that is created. Image File history File links This is a lossless scalable vector image. ...

Paramagnetism

Most popularly found in paper clips, paramagnetism is exhibited in substances which do not emit fields by themselves, but when exposed to a magnetic field, its electrons will begin to spin in such a manner that the substance emits a field of its own. A good analogy for this behavior can be found in a bucket of nails - if you pick up a single nail, you can expect that other nails will not follow. However, you can apply an intense magnetic field to the bucket, pick up one nail, and find that many will come with it. For other uses, see Electron (disambiguation). ...

Main article: Paramagnetism

Simple Illustration of a paramagnetic probe made up from miniature magnets. ...

Diamagnetism

Unscientifically referred to as 'non-magnetic,' diamagnets actually do exhibit some magnetic behavior - just to very small magnitudes. While paramagnetism is affected more by the direction of the spin of electrons, diamagnetism is affected by electrons' centripetal forces. Under the influence of a field, electrons of opposite spin will see opposite effects to their centripetal force: one will increase and one will decrease. This results in a very small magnetic force. All materials exhibit this type of magnetism, however, when diamagnetism pairs with a stronger type of magnetic behavior, the diamagnetic effect is severely overshadowed.

Main article: Diamagnetism

Levitating pyrolytic carbon Diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. ...

Ferromagnetism

This is the 'popular' perception of a magnet. Ferromagnetic materials have a high retainment for magnetization, and a common example is a traditional refrigerator magnet. By technicality, ferromagnetism exists when all of the atoms contribute to the magnetic force emitted. The mechanical explanation of this is similar to that of paramagnetism - the electrons' spins align such it creates a magnetic force. However, unlike paramagnetic substances, a ferromagnet will retain this spin alignment.

Main article: Ferromagnetism

Ferromagnetism is the phenomenon by which materials, such as iron, in an external magnetic field become magnetized and remain magnetized for a period after the material is no longer in the field. ...

Ferrimagnetism

Like ferromagnetism, ferrimagnets retain their magnetization in the absence of a field. However, they are arranged such that some of its atoms oppose the magnetic moment. These atoms are said to be anti-aligned. The first discovered magnetic substance, magnetite, was originally believed to be a ferromagnet; Louis Néel disproved this, however, with the discovery of ferrimagnetism. Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ... Louis Néel (November 22, 1904 - November 14, 2000) is the Nobel Laureate in Physics of 1970. ...

Main article: Ferrimagnetism

In physics, a ferrimagnetic material is one in which the magnetic moment of the atoms on different sublattices oppose as in antiferromagnetism but the opposing moments are unequal and a spontaneous magnetization remains. ...

Antiferromagnetism

When all atoms are arranged in a substance so that they are anti-aligned, the substance is antiferromagnetic. Antiferromagnets have a zero net magnetic moment, meaning no field is emitted by them. Antiferromagnets are less common compared to the other types of behaviors, and are mostly observed at low temperatures. In varying temperatures, antiferromagnets can be seen to exhibit diamagnetic and ferrimagnetic properties.

Main article: Antiferromagnetism

Antiferromagnetic ordering In materials that exhibit antiferromagnetism, the spins of electrons align in a regular pattern with neighboring spins pointing in opposite directions. ...

Units and calculations in magnetism

How we write the laws of magnetism depends on which set of units we employ. For most engineering applications, MKS or SI (Système International) is common. Two other sets, Gaussian and CGS-emu, are the same for magnetic properties, and are commonly used in physics. Look up si, Si, SI in Wiktionary, the free dictionary. ... This article or section is in need of attention from an expert on the subject. ...

In all units it is convenient to employ two types of magnetic field, B and H, as well as the magnetization M, defined as the magnetic moment per unit volume.

(1) The magnetic induction field B is given in SI units of T (tesla). B is the true magnetic field, whose time-variation produces, by Faraday's Law, circulating electric fields (which the power companies sell). B also produces a deflection force on moving charged particles (as in TV tubes). The tesla is equivalent to the magnetic flux (in webers) per unit area (in meters squared), thus giving B the unit of a flux density. In CGS the unit of B is G (gauss). One T equals 10⁴ G.

(2) The magnetic field H is given in SI units of ampere-turns/meter (A-turn/m). The "turns" appears because when H is produced by a current-carrying wire, its value is proportional to the number of turns of that wire. In CGS the unit of H is Oe (oersted). One A-turn/m equals 4π x 10^-3 Oe.

(3) The magnetization M is given in SI units of ampere/meter (A/m). In CGS the unit of M is the emu, or electromagnetic unit. One A/m equals 10^-3 emu. A good permanent magnet can have a magnetization as large as a million A/m. Magnetic fields produced by current-carrying wires would require comparably huge currents per unit length, one reason we employ permanent magnets and electromagnets.

(4) In SI units, the relation B=μ₀(H+M) holds, where μ₀ is the permeability of space, which equals 4π x 10^-7 tesla∙meter/ampere. In CGS it is written as B=H+4πM.

Materials that are not permanent magnets usually satisfy the relation M=χH in SI, where χ is the (dimensionless) magnetic susceptibility. Most non-magnetic materials have a relatively small χ (on the order of a millionth), but soft magnets can have χ's on the order of hundreds or thousands. For materials satisfying M=χH, we can also write B=μ₀(1+χ)H=μ₀μ_rH=μH, where μ_r=1+χ is the (dimensionless) relative permeability and μ = μ₀μ_r is the magnetic permeability. Both hard and soft magnets have a more complex, history-dependent, behavior described by what are called hysteresis loops, which give either B vs H or M vs H. In CGS M=χH, but χ(SI) = 4πχ(CGS), and μ = μ_r.

Caution: In part because there are not enough Roman and Greek symbols, there is no commonly agreed upon symbol for magnetic pole strength and magnetic moment. The symbol m has been used for both pole strength (unit = A-m, where here "m is for meter") and for magnetic moment (unit = A-m²). The symbol μ has been used in some texts for magnetic permeability and in other texts for magnetic moment. We will use μ for magnetic permeability and m for magnetic moment. For pole strength we will employ q_m. For a bar magnet of cross-section A with uniform magnetization M along its axis, the pole strength is given by q_m=MA, so that M can be thought of as a pole strength per unit area.

Calculating the magnetic force

Calculating the attractive or repulsive force between two magnets is, in the general case, an extremely complex operation, as it depends on the shape, magnetization, orientation and separation of the magnets.

Force between two magnetic poles

The force between two magnetic poles is given by:

[1]

where

F is force (SI unit: newton)

q_m1 and q_m2 are the pole strengths (SI unit: ampere-meter)

μ is the permeability of the intervening medium (SI unit: tesla meter per ampere, henry per meter or newton per ampere squared)

r is the separation (SI unit: meter).

The pole description is useful to practicing magneticians who design real-world magnets, but real magnets have a pole distribution more complex than a single north and south. Therefore, implementation of the pole idea is not simple. In some cases, one of the more complex formulae given below will be more useful. For other uses, see Newton (disambiguation). ... The ampere-metre which has the symbol A m or A-m is the SI unit for pole strength in a magnet. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... SI unit. ... This article is about the unit of length. ... For other uses, see Ampere (disambiguation). ...

Force between two nearby attracting surfaces of area A and equal but opposite magnetizations M

[2]

where

A is the area of each surface, in m²

M is their magnetization, in ampere/m.

μ₀ is the permeability of space, which equals 4π x 10^-7 tesla∙meter/ampere

Force between two bar magnets

The force between two identical cylindrical bar magnets placed end-to-end is given by:

[3]

where

B₀ is the magnetic flux density very close to each pole, in T,

A is the area of each pole, in m²,

L is the length of each magnet, in m,

R is the radius of each magnet, in m, and

x is the separation between the two magnets, in m

B₀=M relates the flux density at the pole to the magnetization of the magnet.

See also

A B-H Analyzer is an instrument that measures the AC magnetic characteristics of soft magnetic materials. ... An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... The electromagnetic field is a physical field that is produced by electrically charged objects and which affects the behaviour of charged objects in the vicinity of the field. ... Levitating pyrolytic carbon Diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. ... This article is about the electromagnetic phenomenon. ... In physics, a magnetic monopole is a hypothetical particle that may be loosely described as a magnet with only one pole (see electromagnetic theory for more on magnetic poles). ... For other senses of this word, see magnetism (disambiguation). ... Molecular magnets are systems where a permanent magnetization and magnetic hysteresis can be achieved (although usually at extremely low temperatures) not through a three-dimensional magnetic ordering, but as a purely one-molecule phenomenon. ... Simple Illustration of a paramagnetic probe made up from miniature magnets. ... Magnet therapy, or magnetic therapy, or magnotherapy is a form of alternative medicine involving magnetic fields. ... Supermagnets, as the name suggests, are very powerful magnets. ...

Online references

• HyperPhysics E/M, good complete tree diagram of electromagnetic relationships with magnets
• Maxwell's Equations and some history...
• Detailed Theory on Designing a Solenoid or a Coil Gun

For thermodynamic relations, see Maxwell relations. ...

Printed references

1. "positive pole n." The Concise Oxford English Dictionary. Ed. Catherine Soanes and Angus Stevenson. Oxford University Press, 2004. Oxford Reference Online. Oxford University Press. The Oxford English Dictionary print set The Oxford English Dictionary (OED) is a dictionary published by the Oxford University Press (OUP), and is the most successful dictionary of the English language, (not to be confused with the one-volume Oxford Dictionary of English, formerly New Oxford Dictionary of English, of... Oxford University Press (OUP) is a highly-respected publishing house and a department of the University of Oxford in England. ...

2. Wayne M. Saslow, "Electricity, Magnetism, and Light", Academic (2002). ISBN 0-12-619455-6. Chapter 9 discusses magnets and their magnetic fields using the concept of magnetic poles, but it also gives evidence that magnetic poles don't really exist in ordinary matter. Chapters 10 and 11, following what appears to be a 19th century approach, use the pole concept to obtain the laws describing the magnetism of electric currents.

3. Edward P. Furlani, "Permanent Magnet and Electromechanical Devices: Materials, Analysis and Applications", Academic Press Series in Electromagnetism (2001). ISBN 0-12-269951-3.

References

External links

• Joseph J. Stupak Jr., "Methods of Magnetizing Permanent Magnets"PDF (223 KiB). Oersted Technology at the EMCW Coil Winding Show, 2000.
• Floating Magnet
• Magnets and Electromagnets - Video
• Magnet Technology Center Commercial source of information on permanent magnetic materials.
• Magnet Design Guide Commercial compilation on permanent magnet design.
• Research Papers on Magnetics Commercial company compilation of research papers related to permanent magnets.
• Answers to several questions from curious kids about magnets
• Magnetic units are discussed here
• Kids Konnect - Magnets
• Magnetic separator Overbelt-Overband for iron separation and waste recycling
• Magnetic separator working in a waste recycling plant