A stack of ferrite magnets

Ferrites are electrically non-conductive ferrimagnetic ceramic compound materials, consisting of various mixtures of iron oxides such as Hematite (Fe₂O₃) or Magnetite (Fe₃O₄) and the oxides of other metals. 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. ... 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. ... Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικός (keramikos). ... Iron oxide pigment There are a number of iron oxides: Iron oxides Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites. ... Hematite (AE) or haematite (BE) is the mineral form of Iron(III) oxide, (Fe2O3), one of several iron oxides. ... // Headline text Magnetite is a ferrimagnetic mineral form of iron(II,III) oxide, with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ...

Properties

Ferrites that are used in transformer or electromagnetic cores contain nickel, zinc or Manganese compounds. They have a low coercivity, and are called soft ferrites. Because of their comparatively low losses at high frequencies, they are extensively used in the cores of Switched-Mode Power Supply (SMPS) and RF transformers and inductors. For other uses, see transformers. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... A magnetic core is the core of an electromagnet or inductor. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic and silvery with a gold tinge Atomic mass 58. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ... General Name, Symbol, Number manganese, Mn, 25 Chemical series transition metals Group, Period, Block 7, 4, d Appearance silvery metallic Atomic mass 54. ... In material science, the Coercivity of a ferromagnetic material is the intensity of the magnetic field required to reduce the magnetization of that material to zero after the magnetization of the sample has reached saturation. ... A switched-mode power supply, or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator - an internal control circuit that switches the load current rapidly on and off in order to stabilise the output voltage. ... It has been suggested that this article or section be merged with Radio waves. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ...

In contrast, permanent ferrite magnets (or hard ferrites) have a high remanence after magnetization, and are made with iron oxide and barium and strontium oxides. In a magnetically saturated state they conduct magnetic flux very well and have a high magnetic permeability. This enables these so-called ceramic magnets to store stronger magnetic fields than iron. Remanence is the magnetization left behind in a medium after an external magnetic field is removed. ... General Name, Symbol, Number barium, Ba, 56 Chemical series alkaline earth metals Group, Period, Block 2, 6, s Appearance silvery white Atomic mass 137. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Atomic mass 87. ... For magnetic materials, saturation is the state when the material can not absorb a stronger magnetic field, such that an increase of magnetization produces no significant change in magnetic flux density. ... Magnetic flux, is a measure of quantity of magnetism, taking account of the strength and the extent of a magnetic field. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... Current (I) flowing through a wire produces a magnetic field () around the wire. ...

Today, they are the most commonly used magnets in radios. The maximum magnetic field B is about 0.35 tesla and the magnetic field strength H is about 30 to 160 kiloampere turns per meter (400 to 2000 oersteds). (Hill 2006) SI unit. ... The oersted is old CGS unit of magnetic field strength (or magnetic induction). ...

Ferrites are, as many other ceramics, hard and brittle. They may break easily. A material is brittle if it is subject to fracture when subjected to stress i. ...

Production

Ferrites are produced by a sintering process. A mixed powder is heated and pressed in a mold. This article or section does not cite its references or sources. ...

Permanent magnetic ferrites are formed by a chemical reaction called calcination from the powders of Iron(III) oxide and Barium- or Strontium carbonate. Afterwards the product has to be milled to particles smaller than 2 μm in order to get Weiss domains in the size of one particle. Next the powder is pressed into a shape, dried and sintered. The shaping may be performed in an external magnetic field, in order to achieve a preferred orientation of the particles (anisotropy). Calcination is the process of heating a substance to a high temperature, but below its melting or fusing point, to bring about thermal decomposition or a phase transition in its physical or chemical constitution. ... Iron(III) oxide — also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust — is one of several oxide compounds of iron, and has paramagnetic properties. ... Barium carbonate (BaCO3), also known as witherite, is a chemical compound used in rat poison, bricks and cement. ... Strontianite (SrCO3) is a mineral consisting of strontium carbonate. ... Charge seperation between the positive and negative ions is the reason for electric dipole behavior. ... Look up anisotropy in Wiktionary, the free dictionary. ...

Small and geometrically easy shapes may be produced with dry pressing. However, in such a process small particles may agglomerate and lead to poorer magnetic properties compared to the wet pressing process. As well, direct calcination and sintering without re-milling is possible but leads to poor magnetic properties.

Electromagnets are pre-sintered as well (pre-reaction), milled and pressed. However, the sintering takes place in a specific atmosphere, for instance one with an oxygen shortage). The chemical composition and especially the structure vary strongly between the precursor and the sintered product. General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ...

Uses

Ferrite cores are used in electronic inductors, transformers, and electromagnets where the high electrical resistance of the ferrite leads to very low eddy current losses. They are commonly seen as a lump in a computer cable, called a ferrite bead, which helps to prevent high frequency electrical noise (radio frequency interference) from exiting or entering the equipment. Ferrite bead is a passive electric component used to suppress high frequency noise in electronic circuits. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... For other uses, see transformers. ... An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... As the circular plate moves down through a small region of constant magnetic field directed into the page, eddy currents are induced in the plate. ... Radio Frequency Interference (RFI) is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits. ...

Early computer memories stored data in the residual magnetic fields of hard ferrite cores, which were assembled into arrays of core memory. Ferrite powders are used in the coatings of magnetic recording tapes. One such type of material is iron (III) oxide. The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ... A 16×16 cm area core memory plane of 128×128 bits, i. ... Compact audio cassette Magnetic tape is a non-volatile storage medium consisting of a magnetic coating on a thin plastic strip. ... Iron(III) oxide - also known as ferric oxide, red iron oxide, synthetic maghemite, rouge,or rust - is one of several oxide compounds of iron, and is most notable for its ferromagnetic properties. ...

Ferrite particles are also used as a component of radar-absorbing materials or coatings used in stealth aircraft and in the expensive absorption tiles lining the rooms used for electromagnetic compatibility measurements. F-117 Stealth Fighter Stealth technology covers a range of techniques used with aircraft, ships and missiles, in order to make them less visible (ideally invisible) to radar, infrared and other detection methods. ... Electromagnetic Compatibility (EMC) is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such an energy may induce. ...

Most common radio magnets, including those used in loudspeakers, are ferrite magnets. Ferrite magnets have largely displaced Alnico magnets in these applications. Alnico alloys are composed primarily of cobalt, nickel, and aluminium with the addition of iron, copper, and sometimes titanium. ...

It is a common magnetic material for electromagnetic instrument pickups, because of price and relatively high output. However, such pickups lack certain sonic qualities found in other pickups, such as those that use Alnico alloys or more sophisticated magnets. A picku device acts as a transducer that captures mechanical vibrations (usually from suitably equipped stringed instruments such as the electric guitar, electric bass guitar or electric violin) and converts them to an electronic signal which can be amplified and recorded. ...

External links

• What are the bumps at the end of computer cables?

Sources

• Meeldijk, Victor Electronic Components: Selection and Application Guidelines, 1997 Wiley [ISBN 0-471-18972-3]
• Ott, Henry Noise Reduction Techniques in Electronic Systems 1988 Wiley [ISBN 0-471-85068-3]
• Luecke, Gerald and others General Radiotelephone Operator License Plus Radar Endorsement 2004, Master Pub. [ISBN 0-945053-14-2]
• Bartlett, Bruce and others Practical Recording Techniques 2005 Focal Press [ISBN 0-240-80685-9]
• Hill Technical Sales [1]
• Schaller, George E. Ferrite Processing & Effects on Material Performance [2]