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

Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic susceptibility). However, unlike ferromagnets which are also attracted to magnetic fields, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field. Image File history File links Paramagnetic_probe_without_magnetic_field. ... Image File history File links Paramagnetic_probe_without_magnetic_field. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... This article is about the number one. ... In physics and electrical engineering, the magnetic susceptibility is the degree of magnetization of a material in response to an applied magnetic field. ... 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. ...

Introduction

Constituent atoms or molecules of paramagnetic materials have permanent magnetic moments (dipoles), even in the absence of an applied field. This generally occurs due to the presence of unpaired electrons in the atomic/molecular electron orbitals. In pure paramagnetism, the dipoles do not interact with one another and are randomly oriented in the absence of an external field due to thermal agitation, resulting in zero net magnetic moment. When a magnetic field is applied, the dipoles will tend to align with the applied field, resulting in a net magnetic moment in the direction of the applied field. In the classical description, this alignment can be understood to occur due to a torque being provided on the magnetic moments by an applied field, which tries to align the dipoles parallel to the applied field. However, the truer origins of the alignment can only be understood via the quantum-mechanical properties of spin and angular momentum. The Earths magnetic field, which is approximately a dipole. ... For a less technical and generally accessible introduction to the topic, see Introduction to quantum mechanics. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... This gyroscope remains upright while spinning due to its angular momentum. ...

If there is sufficient energy exchange between neighbouring dipoles they will interact, and may spontaneously align or anti-align and form magnetic domains, resulting in ferromagnetism (permanent magnets) or antiferromagnetism, respectively. Paramagnetic behavior can also be observed in ferromagnetic materials that are above their Curie temperature, and in antiferromagnets above their Néel temperature. 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. ... Antiferromagnetic ordering In materials that exhibit antiferromagnetism, the spins of electrons align in a regular pattern with neighboring spins pointing in opposite directions. ... 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. ... ...

In general paramagnetic effects are quite small: the magnetic susceptibility is of the order of 10⁻³ to 10⁻⁵ for most paramagnets, but may be as high as 10^-1 for synthetic paramagnets such as ferrofluids. In physics and electrical engineering, the magnetic susceptibility is the degree of magnetization of a material in response to an applied magnetic field. ... Ferrofluid on glass, with a magnet underneath. ...

Curie's law

For low levels of magnetisation, the magnetisation of paramagnets is approximated by Curie's law: In a paramagnetic material Curies law relates the magnetization of the material to the applied magnetic field and temperature. ...

where

M is the resulting magnetization

B is the magnetic flux density of the applied field, measured in teslas

T is absolute temperature, measured in kelvins

C is a material-specific Curie constant

This law indicates that the susceptibiliy of paramagnetic materials is inversely proportional to their temperature. However, Curie's law is only valid under conditions of low magnetisation, since it does not consider the saturation of magnetisation that occurs when the atomic dipoles are all aligned in parallel (after everything is aligned, increasing the external field will not increase the total magnetisation since there can be no further alignment). SI unit. ... For other uses, see Kelvin (disambiguation). ... The Curie constant appears in Curies law, which relates the magnetic field and the temperature to the magnetisation of a paramagnetic substans. ...

Paramagnetic materials

Elements

Elements can be paramagnetic if they have unpaired electrons.

The following are some examples of paramagnetic elements:

• Aluminum Al [13] (metal) — Al is the preferred paramagnetic material in theoretical designs of lunar mass driver applications using regolith as an ore.
• Barium Ba [56] (metal)
• Calcium Ca [20] (metal) [Ar]4s2 — diamagnetic
• Oxygen. O [8] (non-metal)
• Platinum Pt [78] (metal)
• Sodium Na [11] (metal)
• Strontium Sr [38] (metal)
• Uranium U [92] (metal)
• Magnesium Mg [12] (metal) 1s2 2s2 2p6 3s2 — diamagnetic
• Technetium Tc [43] (artificial)
• Dysprosium Dy [66] (metal) — ferromagnetic

Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... A mass driver for lunar launch (artists conception) A mass driver or electromagnetic catapult is a method of spacecraft propulsion that would use a linear motor to accelerate payloads up to high speeds. ... Regolith (Greek: blanket rock) is a layer of loose, heterogeneous material covering solid rock. ... For other uses, see Ore (disambiguation). ... For other uses, see Barium (disambiguation). ... For other uses, see Calcium (disambiguation). ... 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. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colourless (gas) colourless (liquid) Standard atomic weight 15. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... For sodium in the diet, see Edible salt. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Standard atomic weight 87. ... This article is about the chemical element. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, Symbol, Number technetium, Tc, 43 Chemical series transition metals Group, Period, Block 7, 5, d Appearance silvery gray metal Standard atomic weight [98](0) g·mol−1 Electron configuration [Kr] 4d5 5s2 Electrons per shell 2, 8, 18, 13, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number dysprosium, Dy, 66 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 162. ... 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. ...

Compounds

Many salts of the d and f transitional metal group show paramagnetic behaviour.

Examples are:

• Copper sulphate
• Dysprosium oxide
• Ferric chloride
• Ferric oxide
• Holmium oxide
• Manganese chloride

Some simple molecules contain unpaired electrons and are thus paramagnetic. The most common is the diatomic oxygen molecule. Copper (II) sulfate (CuSO4) is the most common copper salt, made by the action of sulfuric acid on the base copper oxide. ... Dysprosium Oxide (Dy2O3) is a white, slightly hygroscopic powder having specialized uses in ceramics, glass, phosphors, lasers and dysprosium metal halide lamps. ... R-phrases , S-phrases , Related Compounds Other anions Iron(III) fluoride Iron(III) bromide Other cations Iron(II) chloride Manganese(II) chloride Cobalt(II) chloride Ruthenium(III) chloride Related coagulants Iron(II) sulfate Polyaluminium chloride Except where noted otherwise, data are given for materials in their standard state (at 25... Iron(III) oxide — also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust — is one of the several oxide compounds of iron, and has paramagnetic properties. ... Holmium(III) oxide, a yellow solid, is a compound of holmium sometimes used in making specialty glasses. ... Manganese(II) chloride (MnCl2) is a pink salt derived from the elments manganese and chlorine. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colourless (gas) colourless (liquid) Standard atomic weight 15. ...

See also

• Pierre Curie
• Ferromagnetism

Pierre Curie (May 15, 1859 – died April 19, 1906) was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity. ... 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. ... For other uses, see Magnet (disambiguation). ... 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. ... Superdiamagnetism (or perfect diamagnetism) is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of magnetic susceptibility and the exclusion of the interior magnetic field. ... Superparamagnetism refers to materials which become magnetic in the presence of an external magnet, but revert to a non magnetic state when the external magnet is removed. ... 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. ... Antiferromagnetic ordering In materials that exhibit antiferromagnetism, the spins of electrons align in a regular pattern with neighboring spins pointing in opposite directions. ... 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. ... Metamagnetism is a physical state of matter characterized by a superlinear increase of magnetization over a narrow range of applied magnetic field. ... A spin glass is a disordered material exhibiting high magnetic frustration. ...

References

• Charles Kittel, Introduction to Solid State Physics (Wiley: New York, 1996).
• Neil W. Ashcroft and N. David Mermin, Solid State Physics (Harcourt: Orlando, 1976).
• John David Jackson, Classical Electrodynamics (Wiley: New York, 1999).

External links

• Classification of Magnetic Materials by Applied Alloy Chemistry Group at University of Birmingham.