Magnetism

Magnetic redirects here. For other uses, see Magnetic(disambiguation) and Magnetism (disambiguation).Magnetism is a class of physical phenomena that are

A magnetic quadrupole

mediated by magnetic elds. Electric currents and themagnetic moments of elementary particles give rise toa magnetic eld, which acts on other currents and mag-netic moments. Every material is inuenced to someextent by a magnetic eld. The most familiar eect ison permanent magnets, which have persistent magneticmoments caused by ferromagnetism. Most materials donot have permanent moments. Some are attracted to amagnetic eld (paramagnetism); others are repulsed by amagnetic eld (diamagnetism); others have a more com-plex relationship with an appliedmagnetic eld (spin glassbehavior and antiferromagnetism). Substances that arenegligibly aected by magnetic elds are known as non-magnetic substances. These include copper, aluminium,gases, and plastic. Pure oxygen exhibits magnetic prop-erties when cooled to a liquid state.The magnetic state (or magnetic phase) of a material de-pends on temperature and other variables such as pres-sure and the applied magnetic eld. A material may ex-hibit more than one form of magnetism as these variableschange.

1 HistoryMain article: History of electromagnetismAristotle attributed the rst of what could be called a sci-

Drawing of a medical treatment using magnetic brushes. CharlesJacque 1843, France.

entic discussion onmagnetism to Thales ofMiletus, wholived from about 625 BC to about 545 BC.[1] Around thesame time, in ancient India, the Indian surgeon, Sushruta,was the rst to make use of the magnet for surgicalpurposes.[2]

In ancient China, the earliest literary reference to mag-netism lies in a 4th-century BC book named after its au-thor, The Master of Demon Valley (): The lodestonemakes iron come or it attracts it.[3] The earliest men-tion of the attraction of a needle appears in a work com-posed between AD 20 and 100 (Louen-heng): A lode-stone attracts a needle.[4] The Chinese scientist ShenKuo (10311095) was the rst person to write of themagnetic needle compass and that it improved the accu-racy of navigation by employing the astronomical conceptof true north (Dream Pool Essays, AD 1088), and by the12th century the Chinese were known to use the lode-stone compass for navigation. They sculpted a directionalspoon from lodestone in such a way that the handle of the

1

2 2 SOURCES OF MAGNETISM

spoon always pointed south.Alexander Neckam, by 1187, was the rst in Europe todescribe the compass and its use for navigation. In 1269,Peter Peregrinus de Maricourt wrote the Epistola de mag-nete, the rst extant treatise describing the properties ofmagnets. In 1282, the properties of magnets and the drycompass were discussed by Al-Ashraf, a Yemeni physi-cist, astronomer, and geographer.[5]

Michael Faraday, 1842

In 1600,WilliamGilbert published hisDeMagnete, Mag-neticisque Corporibus, et de Magno Magnete Tellure (Onthe Magnet and Magnetic Bodies, and on the Great Mag-net the Earth). In this work he describes many of his ex-periments with his model earth called the terrella. Fromhis experiments, he concluded that the Earth was itselfmagnetic and that this was the reason compasses pointednorth (previously, some believed that it was the pole star(Polaris) or a large magnetic island on the north pole thatattracted the compass).An understanding of the relationship between electricityand magnetism began in 1819 with work by Hans Chris-tian rsted, a professor at the University of Copenhagen,who discovered more or less by accident that an electriccurrent could inuence a compass needle. This landmarkexperiment is known as rsteds Experiment. Severalother experiments followed, with Andr-Marie Ampre,who in 1820 discovered that the magnetic eld circulatingin a closed-path was related to the current owing throughthe perimeter of the path; Carl Friedrich Gauss; Jean-Baptiste Biot and Flix Savart, both of whom in 1820came up with the BiotSavart law giving an equation forthe magnetic eld from a current-carrying wire; Michael

Faraday, who in 1831 found that a time-varying magneticux through a loop of wire induced a voltage, and othersnding further links between magnetism and electricity.James Clerk Maxwell synthesized and expanded these in-sights intoMaxwells equations, unifying electricity, mag-netism, and optics into the eld of electromagnetism. In1905, Einstein used these laws in motivating his theoryof special relativity,[6] requiring that the laws held true inall inertial reference frames.Electromagnetism has continued to develop into the 21stcentury, being incorporated into the more fundamen-tal theories of gauge theory, quantum electrodynamics,electroweak theory, and nally the standard model.

2 Sources of magnetismSee also: Magnetic moment

Magnetism, at its root, arises from two sources:

1. Electric current (see Electron magnetic moment).

2. Spin magnetic moments of elementary particles.The magnetic moments of the nuclei of atoms aretypically thousands of times smaller than the elec-trons magnetic moments, so they are negligible inthe context of the magnetization of materials. Nu-clear magnetic moments are very important in othercontexts, particularly in nuclear magnetic resonance(NMR) and magnetic resonance imaging (MRI).

Ordinarily, the enormous number of electrons in a mate-rial are arranged such that their magnetic moments (bothorbital and intrinsic) cancel out. This is due, to some ex-tent, to electrons combining into pairs with opposite in-trinsic magnetic moments as a result of the Pauli exclu-sion principle (see electron conguration), or combininginto lled subshells with zero net orbital motion. In bothcases, the electron arrangement is so as to exactly can-cel the magnetic moments from each electron. Moreover,even when the electron conguration is such that there areunpaired electrons and/or non-lled subshells, it is oftenthe case that the various electrons in the solid will con-tribute magnetic moments that point in dierent, randomdirections, so that the material will not be magnetic.However, sometimeseither spontaneously, or owing toan applied external magnetic eldeach of the electronmagnetic moments will be, on average, lined up. Thenthe material can produce a net total magnetic eld, whichcan potentially be quite strong.The magnetic behavior of a material depends on its struc-ture, particularly its electron conguration, for the rea-sons mentioned above, and also on the temperature. Athigh temperatures, random thermalmotionmakes it moredicult for the electrons to maintain alignment.

3.2 Paramagnetism 3

3 Materials

Diamagnetism: Property of all

matter

Uncompensated orbital and spin

angular momentum

Permanent atomic moments

Independent atomic moments

Ideal paramagnetism

Cooperating atomic moments

Ferromagnetism Antiferromagneti sm Ferrimagnetism

Electronic bands in metals

Pauli spin paramagnetism

Band antiferromagneti sm

Band ferromagnetism

Hierarchy of types of magnetism.[7]

3.1 Diamagnetism

Main article: Diamagnetism

Diamagnetism appears in all materials, and is the ten-dency of a material to oppose an applied magnetic eld,and therefore, to be repelled by a magnetic eld. How-ever, in a material with paramagnetic properties (that is,with a tendency to enhance an external magnetic eld),the paramagnetic behavior dominates.[8] Thus, despite itsuniversal occurrence, diamagnetic behavior is observedonly in a purely diamagnetic material. In a diamagneticmaterial, there are no unpaired electrons, so the intrin-sic electron magnetic moments cannot produce any bulkeect. In these cases, the magnetization arises fromthe electrons orbital motions, which can be understoodclassically as follows:

When a material is put in a magnetic eld,the electrons circling the nucleus will experi-ence, in addition to their Coulomb attractionto the nucleus, a Lorentz force from the mag-netic eld. Depending on which direction theelectron is orbiting, this force may increasethe centripetal force on the electrons, pullingthem in towards the nucleus, or it may decreasethe force, pulling them away from the nucleus.This eect systematically increases the orbitalmagnetic moments that were aligned oppositethe eld, and decreases the ones aligned paral-lel to the eld (in accordance with Lenzs law).This results in a small bulk magnetic moment,with an opposite direction to the applied eld.

Note that this description is meant only as an heuristic;a proper understanding requires a quantum-mechanicaldescription.Note that all materials undergo this orbital response.However, in paramagnetic and ferromagnetic substances,

the diamagnetic eect is overwhelmed by the muchstronger eects caused by the unpaired electrons.

3.2 ParamagnetismMain article: Paramagnetism

In a paramagnetic material there are unpaired electrons,i.e. atomic or molecular orbitals with exactly one electronin them. While paired electrons are required by the Pauliexclusion principle to have their intrinsic ('spin') mag-netic moments pointing in opposite directions, causingtheir magnetic elds to cancel out, an unpaired electron isfree to align its magnetic moment in any direction. Whenan external magnetic eld is applied, these magnetic mo-ments will tend to align themselves in the same directionas the applied eld, thus reinforcing it.

3.3 Ferromagnetism

A permanent magnet holding up several coins

Main article: Ferromagnetism

A ferromagnet, like a paramagnetic substance, has un-paired electrons. However, in addition to the electronsintrinsic magnetic moments tendency to be parallel to anapplied eld, there is also in thesematerials a tendency forthese magnetic moments to orient parallel to each otherto maintain a lowered-energy state. Thus, even in the ab-sence of an applied eld, the magnetic moments of theelectrons in the material spontaneously line up parallel toone another.Every ferromagnetic substance has its own individualtemperature, called the Curie temperature, or Curiepoint, above which it loses its ferromagnetic properties.This is because the thermal tendency to disorder over-whelms the energy-lowering due to ferromagnetic order.Ferromagnetism only occurs in a few substances; thecommon ones are iron, nickel, cobalt, their alloys, and

4 3 MATERIALS

some alloys of rare earth metals.

3.3.1 Magnetic domains

Magnetic domains boundaries (white lines) in ferromagnetic ma-terial (black rectangle).

Main article: Magnetic domains

Themagneticmoments of atoms in a ferromagneticmate-rial cause them to behave something like tiny permanentmagnets. They stick together and align themselves intosmall regions of more or less uniform alignment calledmagnetic domains or Weiss domains. Magnetic domainscan be observed with a magnetic force microscope toreveal magnetic domain boundaries that resemble whitelines in the sketch. There are many scientic experimentsthat can physically show magnetic elds.When a domain contains too many molecules, it becomesunstable and divides into two domains aligned in oppositedirections so that they stick together more stably as shownat the right.When exposed to a magnetic eld, the domain bound-aries move so that the domains aligned with the magneticeld grow and dominate the structure (dotted yellow area)as shown at the left. When the magnetizing eld is re-moved, the domains may not return to an unmagnetizedstate. This results in the ferromagnetic materials beingmagnetized, forming a permanent magnet.When magnetized strongly enough that the prevailing do-main overruns all others to result in only one single do-main, the material is magnetically saturated. When amagnetized ferromagnetic material is heated to the Curiepoint temperature, the molecules are agitated to the pointthat the magnetic domains lose the organization and themagnetic properties they cause cease. When the materialis cooled, this domain alignment structure spontaneously

Eect of a magnet on the domains.

returns, in a manner roughly analogous to how a liquidcan freeze into a crystalline solid.

3.4 Antiferromagnetism

Antiferromagnetic ordering

Main article: Antiferromagnetism

In an antiferromagnet, unlike a ferromagnet, there is atendency for the intrinsic magnetic moments of neigh-boring valence electrons to point in opposite directions.When all atoms are arranged in a substance so that eachneighbor is 'anti-aligned', the substance is antiferromag-netic. Antiferromagnets have a zero net magnetic mo-ment, meaning no eld is produced by them. Antiferro-magnets are less common compared to the other types ofbehaviors, and are mostly observed at low temperatures.In varying temperatures, antiferromagnets can be seen toexhibit diamagnetic and ferrimagnetic properties.In some materials, neighboring electrons want to point inopposite directions, but there is no geometrical arrange-ment in which each pair of neighbors is anti-aligned. Thisis called a spin glass, and is an example of geometricalfrustration.

53.5 Ferrimagnetism

Ferrimagnetic ordering

Main article: Ferrimagnetism

Like ferromagnetism, ferrimagnets retain their magne-tization in the absence of a eld. However, like antiferro-magnets, neighboring pairs of electron spins like to pointin opposite directions. These two properties are not con-tradictory, because in the optimal geometrical arrange-ment, there is more magnetic moment from the sublat-tice of electrons that point in one direction, than from thesublattice that points in the opposite direction.Most ferrites are ferrimagnetic. The rst discoveredmag-netic substance, magnetite, is a ferrite and was originallybelieved to be a ferromagnet; Louis Nel disproved this,however, after discovering ferrimagnetism.

3.6 Superparamagnetism

Main article: Superparamagnetism

When a ferromagnet or ferrimagnet is suciently small, itacts like a single magnetic spin that is subject to Brownianmotion. Its response to a magnetic eld is qualitativelysimilar to the response of a paramagnet, but much larger.

3.7 Other types of magnetism

Metamagnetism

Molecule-based magnet

Spin glass

4 ElectromagnetAn electromagnet is a type of magnet whose magnetismis produced by the ow of electric current. The magneticeld disappears when the current ceases.

An electromagnet attracts paper clips when current is applied cre-ating a magnetic eld. The electromagnet loses them when cur-rent and magnetic eld are removed.

5 Magnetism, electricity, and spe-cial relativity

Main article: Classical electromagnetism and special rel-ativityAs a consequence of Einsteins theory of special rela-

Magnetism from length-contraction.

tivity, electricity and magnetism are fundamentally in-terlinked. Both magnetism lacking electricity, and elec-tricity without magnetism, are inconsistent with spe-cial relativity, due to such eects as length contrac-tion, time dilation, and the fact that the magnetic forceis velocity-dependent. However, when both electricityand magnetism are taken into account, the resulting the-ory (electromagnetism) is fully consistent with specialrelativity.[6][9] In particular, a phenomenon that appearspurely electric or purely magnetic to one observer maybe a mix of both to another, or more generally the rela-tive contributions of electricity andmagnetism are depen-dent on the frame of reference. Thus, special relativitymixes electricity and magnetism into a single, insepa-rable phenomenon called electromagnetism, analogous tohow relativity mixes space and time into spacetime.All observations on electromagnetism apply to what

6 7 MAGNETIC FORCE

might be considered to be primarily magnetism, e.g. per-turbations in the magnetic eld are necessarily accompa-nied by a nonzero electric eld, and propagate at the speedof light.

6 Magnetic elds in a materialSee also: Magnetic eld H and B inside and outside ofmagnetic materials

In a vacuum,

B = 0H;

where 0 is the vacuum permeability.In a material,

B = 0(H+M):

The quantity 0M is called magnetic polarization.If the eld H is small, the response of the magnetizationM in a diamagnet or paramagnet is approximately linear:

M = H;

the constant of proportionality being called the magneticsusceptibility. If so,

0(H+M) = 0(1 + )H = r0H = H:

In a hard magnet such as a ferromagnet,M is not propor-tional to the eld and is generally nonzero even when His zero (see Remanence).

7 Magnetic forceMain article: Magnetic eld

The phenomenon of magnetism is mediated by themagnetic eld. An electric current or magnetic dipolecreates a magnetic eld, and that eld, in turn, impartsmagnetic forces on other particles that are in the elds.Maxwells equations, which simplify to the BiotSavartlaw in the case of steady currents, describe the origin andbehavior of the elds that govern these forces. Therefore,magnetism is seen whenever electrically charged particlesare in motionfor example, frommovement of electronsin an electric current, or in certain cases from the or-bital motion of electrons around an atoms nucleus. They

Magnetic lines of force of a bar magnet shown by iron lings onpaper

also arise from intrinsic magnetic dipoles arising fromquantum-mechanical spin.The same situations that create magnetic eldschargemoving in a current or in an atom, and intrinsic magneticdipolesare also the situations in which a magnetic eldhas an eect, creating a force. Following is the formulafor moving charge; for the forces on an intrinsic dipole,see magnetic dipole.When a charged particle moves through a magnetic eldB, it feels a Lorentz force F given by the cross product:[10]

F = q(v B)

where

q is the electric charge of the particle, andv is the velocity vector of the particle

Because this is a cross product, the force is perpendicularto both the motion of the particle and the magnetic eld.It follows that themagnetic force does no work on the par-ticle; it may change the direction of the particles move-ment, but it cannot cause it to speed up or slow down. Themagnitude of the force is

F = qvB sin

where is the angle between v and B.One tool for determining the direction of the velocity vec-tor of a moving charge, the magnetic eld, and the forceexerted is labeling the index nger V, the middle n-ger B, and the thumb F with your right hand. Whenmaking a gun-like conguration, with the middle ngercrossing under the index nger, the ngers represent thevelocity vector, magnetic eld vector, and force vector,respectively. See also right hand rule.

78 Magnetic dipolesMain article: Magnetic dipole

A very common source of magnetic eld shown in natureis a dipole, with a "South pole" and a "North pole", termsdating back to the use of magnets as compasses, inter-acting with the Earths magnetic eld to indicate Northand South on the globe. Since opposite ends of mag-nets are attracted, the north pole of a magnet is attractedto the south pole of another magnet. The Earths NorthMagnetic Pole (currently in the Arctic Ocean, north ofCanada) is physically a south pole, as it attracts the northpole of a compass. A magnetic eld contains energy, andphysical systems move toward congurations with lowerenergy. When diamagnetic material is placed in a mag-netic eld, a magnetic dipole tends to align itself in op-posed polarity to that eld, thereby lowering the net eldstrength. When ferromagnetic material is placed within amagnetic eld, the magnetic dipoles align to the appliedeld, thus expanding the domain walls of the magneticdomains.

8.1 Magnetic monopoles

Main article: Magnetic monopole

Since a bar magnet gets its ferromagnetism from elec-trons distributed evenly throughout the bar, when a barmagnet is cut in half, each of the resulting pieces is asmaller bar magnet. Even though a magnet is said tohave a north pole and a south pole, these two poles can-not be separated from each other. A monopoleif sucha thing existswould be a new and fundamentally dier-ent kind of magnetic object. It would act as an isolatednorth pole, not attached to a south pole, or vice versa.Monopoles would carry magnetic charge analogous toelectric charge. Despite systematic searches since 1931,as of 2010, they have never been observed, and could verywell not exist.[11]

Nevertheless, some theoretical physics models predict theexistence of these magnetic monopoles. Paul Dirac ob-served in 1931 that, because electricity and magnetismshow a certain symmetry, just as quantum theory predictsthat individual positive or negative electric charges can beobserved without the opposing charge, isolated South orNorth magnetic poles should be observable. Using quan-tum theory Dirac showed that if magnetic monopoles ex-ist, then one could explain the quantization of electricchargethat is, why the observed elementary particlescarry charges that are multiples of the charge of the elec-tron.Certain grand unied theories predict the existenceof monopoles which, unlike elementary particles, aresolitons (localized energy packets). The initial re-

sults of using these models to estimate the number ofmonopoles created in the big bang contradicted cosmo-logical observationsthe monopoles would have been soplentiful and massive that they would have long sincehalted the expansion of the universe. However, the ideaof ination (for which this problem served as a partial mo-tivation) was successful in solving this problem, creatingmodels in which monopoles existed but were rare enoughto be consistent with current observations.[12]

9 Quantum-mechanical origin ofmagnetism

In principle all kinds of magnetism originate (similarto superconductivity) from specic quantum-mechanicalphenomena (e.g. Mathematical formulation of quantummechanics, in particular the chapters on spin and on thePauli principle). A successful model was developed al-ready in 1927, by Walter Heitler and Fritz London, whoderived quantum-mechanically, how hydrogen moleculesare formed from hydrogen atoms, i.e. from the atomic hy-drogen orbitals uA and uB centered at the nuclei A andB, see below. That this leads to magnetism is not at allobvious, but will be explained in the following.According to the Heitler-London theory, so-called two-body molecular -orbitals are formed, namely the re-sulting orbital is:

(r1; r2) =1p2

(uA(r1)uB(r2) + uB(r1)uA(r2))

Here the last product means that a rst electron, r1, isin an atomic hydrogen-orbital centered at the second nu-cleus, whereas the second electron runs around the rstnucleus. This exchange phenomenon is an expressionfor the quantum-mechanical property that particles withidentical properties cannot be distinguished. It is specicnot only for the formation of chemical bonds, but as wewill see, also for magnetism, i.e. in this connection theterm exchange interaction arises, a term which is essen-tial for the origin of magnetism, and which is stronger,roughly by factors 100 and even by 1000, than the ener-gies arising from the electrodynamic dipole-dipole inter-action.As for the spin function (s1; s2) , which is responsiblefor the magnetism, we have the already mentioned Paulisprinciple, namely that a symmetric orbital (i.e. with the +sign as above) must be multiplied with an antisymmetricspin function (i.e. with a sign), and vice versa. Thus:

(s1; s2) =1p2

((s1)(s2) (s1)(s2))

I.e., not only uA and uB must be substituted by and, respectively (the rst entity means spin up, the sec-ond one spin down), but also the sign + by the sign,

8 13 REFERENCES

and nally r by the discrete values s (= ); therebywe have (+1/2) = (1/2) = 1 and (1/2) =(+1/2) = 0 . The "singlet state", i.e. the sign,means: the spins are antiparallel, i.e. for the solid wehave antiferromagnetism, and for two-atomic moleculesone has diamagnetism. The tendency to form a (ho-moeopolar) chemical bond (this means: the formation ofa symmetric molecular orbital, i.e. with the + sign) re-sults through the Pauli principle automatically in an an-tisymmetric spin state (i.e. with the sign). In contrast,the Coulomb repulsion of the electrons, i.e. the tendencythat they try to avoid each other by this repulsion, wouldlead to an antisymmetric orbital function (i.e. with the sign) of these two particles, and complementary to asymmetric spin function (i.e. with the + sign, one of theso-called "triplet functions"). Thus, now the spins wouldbe parallel (ferromagnetism in a solid, paramagnetism intwo-atomic gases).The last-mentioned tendency dominates in the metalsiron, cobalt and nickel, and in some rare earths, which areferromagnetic. Most of the other metals, where the rst-mentioned tendency dominates, are nonmagnetic (e.g.sodium, aluminium, and magnesium) or antiferromag-netic (e.g. manganese). Diatomic gases are also almostexclusively diamagnetic, and not paramagnetic. How-ever, the oxygen molecule, because of the involvement of-orbitals, is an exception important for the life-sciences.The Heitler-London considerations can be generalized tothe Heisenberg model of magnetism (Heisenberg 1928).The explanation of the phenomena is thus essentiallybased on all subtleties of quantum mechanics, whereasthe electrodynamics covers mainly the phenomenology.

10 Units

10.1 SI

10.2 Other

gauss the centimeter-gram-second (CGS) unit ofmagnetic eld (denoted B).

oersted the CGS unit ofmagnetizing eld (denotedH).

maxwell the CGS unit for magnetic ux.

gamma a unit of magnetic ux density that wascommonly used before the tesla came into use (1.0gamma = 1.0 nanotesla)

0 common symbol for the permeability of freespace (4107 newton/(ampere-turn)2).

11 Living thingsSome organisms can detect magnetic elds, a phe-nomenon known as magnetoception. Magnetobiologystudies magnetic elds as a medical treatment; eldsnaturally produced by an organism are known asbiomagnetism.

12 See also Coercivity Magnetic hysteresis Magnetar Magnetic bearing Magnetic circuit Magnetic cooling Magnetic eld viewing lm Magnetic stirrer Magnetic structure Magnetism and temperature Micromagnetism Neodymium magnet Plastic magnet Rare-earth magnet Spin wave Spontaneous magnetization Vibrating sample magnetometer Gravitomagnetism

13 References[1] Fowler, Michael (1997). Historical Beginnings of The-

ories of Electricity and Magnetism. Retrieved 2008-04-02.

[2] Vowles, Hugh P. (1932). Early Evolution of Power Engi-neering. Isis (University of Chicago Press) 17 (2): 412420 [41920]. doi:10.1086/346662.

[3] Li Shu-hua, Origine de la Boussole 11. Aimant et Bous-sole, Isis, Vol. 45, No. 2. (Jul., 1954), p.175

[4] Li Shu-hua, Origine de la Boussole 11. Aimant et Bous-sole, Isis, Vol. 45, No. 2. (Jul., 1954), p.176

9[5] Schmidl, Petra G. (19961997). Two Early ArabicSources On The Magnetic Compass. Journal of Arabicand Islamic Studies 1: 81132.

[6] A. Einstein: On the Electrodynamics ofMoving Bodies,June 30, 1905.

[7] HPMeyers (1997). Introductory solid state physics (2 ed.).CRC Press. p. 362; Figure 11.1. ISBN 9781420075021.

[8] Catherine Westbrook, Carolyn Kaut, Carolyn Kaut-Roth(1998). MRI (Magnetic Resonance Imaging) in practice (2ed.). Wiley-Blackwell. p. 217. ISBN 0-632-04205-2.

[9] Griths 1998, chapter 12

[10] Jackson, John David (1999). Classical electrodynamics(3rd ed.). New York: Wiley. ISBN 0-471-30932-X.

[11] Milton mentions some inconclusive events (p.60) andstill concludes that no evidence at all of magneticmonopoles has survived (p.3). Milton, Kimball A.(June 2006). Theoretical and experimental statusof magnetic monopoles. Reports on Progress inPhysics 69 (6): 16371711. arXiv:hep-ex/0602040.Bibcode:2006RPPh...69.1637M. doi:10.1088/0034-4885/69/6/R02..

[12] Guth, Alan (1997). The Inationary Universe: The Questfor a New Theory of Cosmic Origins. Perseus. ISBN 0-201-32840-2. OCLC 38941224..

[13] International Union of Pure and Applied Chemistry(1993). Quantities, Units and Symbols in Physical Chem-istry, 2nd edition, Oxford: Blackwell Science. ISBN 0-632-03583-8. pp. 1415. Electronic version.

14 Further reading Furlani, Edward P. (2001). Permanent Magnet andElectromechanical Devices: Materials, Analysis andApplications. Academic Press. ISBN 0-12-269951-3. OCLC 162129430.

Griths, David J. (1998). Introduction to Electro-dynamics (3rd ed.). Prentice Hall. ISBN 0-13-805326-X. OCLC 40251748.

Kronmller, Helmut. (2007). Handbook of Mag-netism and Advanced Magnetic Materials, 5 VolumeSet. JohnWiley & Sons. ISBN 978-0-470-02217-7.OCLC 124165851.

Tipler, Paul (2004). Physics for Scientists and Engi-neers: Electricity, Magnetism, Light, and ElementaryModern Physics (5th ed.). W. H. Freeman. ISBN0-7167-0810-8. OCLC 51095685.

David K. Cheng (1992). Field and Wave Electro-magnetics. Addison-Wesley Publishing Company,Inc. ISBN 0-201-12819-5.

15 External links Magnetism on In Our Time at the BBC. (listen now) The Exploratorium Science Snacks Snacks aboutMagnetism

Electromagnetism - a chapter from an online text-book

Video: The physicist Richard Feynman answers thequestion, Why do bar magnets attract or repel eachother? on YouTube

On the Magnet, 1600 First scientic book on mag-netism by the father of electrical engineering. FullEnglish text, full text search.

Magnetism and magnetization - Astronoo

10 16 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

16 Text and image sources, contributors, and licenses16.1 Text

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History Sources of magnetism Materials Diamagnetism Paramagnetism Ferromagnetism Magnetic domains

Antiferromagnetism Ferrimagnetism SuperparamagnetismOther types of magnetism

ElectromagnetMagnetism, electricity, and special relativity Magnetic fields in a material Magnetic force Magnetic dipoles Magnetic monopoles

Quantum-mechanical origin of magnetism Units SI Other

Living things See also References Further reading External links Text and image sources, contributors, and licensesTextImagesContent license