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Ferromagnetism - Ferromagnetism Fe omagne i m I L.S...

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Unformatted text preview: 1/22/12 Ferromagnetism Fe omagne i m I , , ( , ) ( L ) .S - F . .W , , .F , , .T .T , . I F .T " " .T , . A .T C . F , .T , 60 H AC . M T T H P , ***** C C M h perph sics.ph -astr.gsu.edu/hbase/solids/ferro.html#c4 ***** E M R Na e GB 1/6 1/22/12 Ferromagnetism Long Range O de in Fe omagne The g a ge de hich c ea e ag e ic d ai i fe ag e ic a e ia aie f aa echa ica i e ac i a he a ic e e . Thi i e ac i i e a ab e i ha i c he ag e ic e f eighb i g a i a igid I de a a e de e a a ge be f a i i e f he he a agi a i hich ed a d i e a a ic- e e de . Si e f d ai a ge f a 0.1 Refe e ce a fe . Whe a e e a ag e ic fie d i a ied, he d ai a ead Oha ia a ig ed i he di ec i f hi fie d g a he e e e f hei eighb . If a he Sec 33- 3 i e e a ig ed i a iece f i , he fie d d be ab 2.1 Te a. A ag e ic fie d f ab 1 T ca be d ced i a ea ed i i h a e e a fie d f ab 0.0002 T, a i ica i f he e e a fie d b a fac f 5000! F a gi e fe ag e ic a e ia he g a ge de ab di a ea a a ce ai e e a e hich i ca ed he C ie e e a e f he a e ia . The C ie e e a e f i i ab 1043 K. H e Ph ic ***** C de ed Ma e ***** E ec ici a d Mag e i The C ie Tempe a F ce C f A R Na e e a gi e fe ag e ic a e ia he g a ge de ab di a ea a a ai e e a e hich i ca ed he C ie e e a e f he a e ia . The ie e e a e f i i ab 1043 K. The C ie e e a e gi e a idea he a fe e g a e b ea he g- a ge de i g i he a e ia . 1043 K he he a e e g i ab 0.135 eV c a ed ab 0.04 eV a e e a e. Mag e ic e ie f id Tab e f C ie e I de ea e H e Ph ic ***** C de ed Ma e ***** E ec ici a d Mag e i h perph sics.ph -astr.gsu.edu/hbase/solids/ferro.html#c4 G Bac R Na e G Bac 2/6 1/22/12 Ferromagnetism Magne ic Domain The mic o copic o de ing of elec on pin cha ac e i ic of fe omagne ic ma e ial lead o he fo ma ion of egion of magne ic alignmen called domain . The main implica ion of he domain i ha he e i al ead a high deg ee of magne i a ion in fe omagne ic ma e ial i hin indi id al domain , b ha in he ab ence of e e nal magne ic field ho e domain a e andoml o ien ed. A mode applied magne ic field can ca e a la ge deg ee of alignmen of he magne ic momen i h he e e nal field, gi ing a la ge m l iplica ion of he applied field. The e ill a ion of domain a e concep al onl and no mean o gi e an acc a e Inde cale of he i e o hape of domain . The mic o copic e idence abo magne i a ion indica e ha he ne magne i a ion of fe omagne ic ma e ial in e pon e o an Refe ence e e nal magne ic field ma ac all occ mo e b he g o h of he domain pa allel Yo ng o he applied field a he e pen e of o he domain a he han he eo ien a ion of Sec 29- 8 he domain hem el e a implied in he ke ch. Me Ch. 11 Some of he mo e di ec e idence e ha e abo domain come f om imaging of domain in ingle c al of fe omagne ic ma e ial . The ke che abo e a e af e h perph sics.ph -astr.gsu.edu/hbase/solids/ferro.html#c4 3/6 1/22/12 Ferromagnetism Young and are adapted from magnified images of domain boundaries in single crystals of nickel. They suggest that the effect of external magnetic fields is to cause the domain boundaries to shift in favor of those domains which are parallel to the applied field. It is not clear how this applies to bulk magnetic materials which are polycrystalline. Keep in mind the fact that the internal magnetic fields which come from the long range ordering of the electron spins are much stronger, sometimes hundreds of times stronger, than the external magnetic fields required to produce these changes in domain alignment. The effective multiplication of the external field which can be achieved by the alignment of the domains is often expressed in terms of the relative permeability. Domains may be made visible with the use of magnetic colloidal suspensions which concentrate along the domain boundaries. The domain boundaries can be imaged by polarized light, and also with the use of electron diffraction. Observation of domain boundary movement under the influence of applied magnetic fields has aided in the development of theoretical treatments. It has been demonstrated that the formation of domains minimizes the magnetic contribution to the free energy. HyperPhysics***** Condensed Matter ***** Electricity and Magnetism R Na e Go Back Relative Permeabilit The magnetic constant μ0 = 4 x 10-7 T m/A is called the permeability of space. The permeabilities of most materials are very close to μ0 since most materials will be classified as either paramagnetic or diamagnetic. But in ferromagnetic materials the permeability may be very large and it is convenient to characterize the materials by a relative permeability. Table of magnetic properties Index When ferromagnetic materials are used in applications like an iron- core solenoid, h perph sics.ph -astr.gsu.edu/hbase/solids/ferro.html#c4 4/6 1/22/12 Ferromagnetism .S 200 .T , , . M H P ***** C M ***** E M R Na e GB Applica ion of Fe omagne i m Elec omagne I Magne ic ape eco ding T an fo me F H P ***** C M h perph sics.ph -astr.gsu.edu/hbase/solids/ferro.html#c4 ***** E M R Na e GB 5/6 1/22/12 h perph sics.ph -astr.gsu.edu/hbase/solids/ferro.html#c4 Ferromagnetism 6/6 ...
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