材料的磁性能

材料的磁性能第1页，课件共20页，创作于2023年2月ContentsOpticalPropertiesElectricalPropertiesThermalPropertiesMagneticProperties第2页，课件共20页，创作于2023年2月OtherPropertiesofMaterials(ForSelf-Study)ElectricalProperties：Thermoelectric,PyroelectricandMagnetoelectricProperty(热电、热释电、磁电性能)MagneticProperties：Magnetostriction

andMagnetoresistance(磁致伸缩、磁电阻)OpticalProperties:Electrooptic,Photoelectric

andMagnetoopticProperty(电光、光电、磁光性能)Acoustic

Properties:

Propagation,AbsorptionandElectroacousticProperty(声音的传播、吸收、电声性能)Elasticity:Anelasticity

andInternalFriction(滞弹性与内耗)第3页，课件共20页，创作于2023年2月4.MagneticProperties4.1BASICCONCEPTSMagneticDipoles(磁偶极子):

smallbarmagnetscomposedofnorthandsouth.Magneticforces(fields)aregeneratedbymovingelectricallychargedparticles.MagneticfieldlinesofforcearoundacurrentloopandabarmagnetThemagneticmomentasdesignatedbyanarrow第4页，课件共20页，创作于2023年2月Magneticfieldstrength(磁场强度)H:theexternallyappliedmagneticfield.H=NI/l(4.1)Acylindricalcoil(orsolenoid):Ncloselyspacedturns,lengthl,currentofmagnitudeI.UnitofH:amperespermeter.Magneticfieldstrengthwithinacoil—dependenceonnumberofturns,appliedcurrent,andcoillength.Magneticinduction(磁感应强度)/magneticfluxdensity(磁通密度)B:themagnitudeoftheinternalfieldstrengthwithinasubstancethatissubjectedtoanHfield.B=μH(4.2)Permeability(磁导率)μ:ThepropertyofthespecificmediumthroughwhichtheHfieldpassesandinwhichBismeasured.Thepermeabilityhasdimensionsofwebersperampere-meter(Wb/Am)orhenriespermeter(H/m).BothBandHarefieldvectors.Magneticfluxdensityinamaterial—dependenceonpermeabilityandmagneticfieldstrength.第5页，课件共20页，创作于2023年2月Inavacuum:B0=μ0H(4.3)Permeabilityofavacuum(真空磁导率)μ0:

auniversalconstant,whichhasavalueof4π

x10-7(1.257x10-6)H/m.B0:thefluxdensitywithinavacuum.μr=μ/μ0

(4.4)Relativepermeability(相对磁导率)μr:ameasureofthedegreetowhichthematerialcanbemagnetized,ortheeasewithwhichaBfieldcanbeinducedinthepresenceofanexternalHfield.AcoilandtheH,B第6页，课件共20页，创作于2023年2月Magnetization(磁化强度)M:B=μ0H+μ0M(4.5)Magneticsusceptibility(磁化率)

χm,(unitless):M=

χmH(4.6)Magnetizationofamaterial—dependenceonsusceptibilityandmagneticfieldstrength.Relationshipbetweenmagneticsusceptibilityandrelativepermeability:χm=μr-1

(4.7)OriginsofMagneticMomentsEachelectroninanatomhasmagneticmomentsthatoriginatefromtwosources:orbitalmomentsandspinmoments.Ineachindividualatom,orbitalmomentsofsomeelectronpairscanceleachother;thisalsoholdsforthespinmoments.Thenetmagneticmomentforanatomisthesumofthemagneticmomentsofeachoftheconstituentelectrons,includingbothorbitalandspincontributions,andtakingintoaccountmomentcancellation.Foranatomhavingcompletelyfilledelectronshellsorsubshells,thereistotalcancellationofbothorbitalandspinmoments,andisnotcapableofbeingpermanentlymagnetized(He,Ne,Ar,etc.).第7页，课件共20页，创作于2023年2月4.2DIAMAGNETISMANDPARAMAGNETISMDiamagnetism(抗磁性/逆磁性/反磁性)Veryweakformofmagnetismthatisnonpermanent,andpersistsonlywhileanexternalfieldisbeingapplied.Inducedbyachangeintheorbitalmotionofelectronsduetoanappliedmagneticfield.Themagnitudeoftheinducedmagneticmomentisextremelysmall,andinadirectionoppositetothatoftheappliedfield.μrislessthanunity(onlyveryslightly),andχm

isnegative;Bislessthanthatinavacuum,χm

isontheorderof-10-5.AtomicdipoleconfigurationforadiamagneticmaterialWhenplacedbetweenthepolesofastrongelectromagnet,diamagneticmaterialsareattractedtowardregionswherethefieldisweak.Thisformofmagnetismisofnopracticalimportance.第8页，课件共20页，创作于2023年2月Paramagnetism(顺磁性)Eachatompossessesapermanentdipolemomentbyvirtueofincompletecancellationofelectronspinand/ororbitalmagneticmoments.Intheabsenceofanexternalmagneticfield,theorientationsoftheseatomicmagneticmomentsarerandom,suchthatapieceofmaterialpossessesnonetmacroscopicmagnetization.Atomicdipolesarefreetorotate,andactedonindividuallywithnomutualinteractionbetweenadjacentdipoles.μrisgreaterthanunity,andtoarelativelysmallbutpositivemagneticsusceptibility.χmrangefromabout10-5to10-2.Bothdiamagneticandparamagneticmaterialsareconsiderednonmagnetic.AtomicdipoleconfigurationforaparamagneticmaterialSchematicrepresentationofB-Hfordiamagneticandparamagneticmaterials第9页，课件共20页，创作于2023年2月4.3FERROMAGNETISMFerromagnetism(铁磁性):

Apermanentmagneticmomentintheabsenceofanexternalfield,andmanifestverylargeandpermanentmagnetizations.Fe(asα-ferrite),Co,Ni,andsomeoftherareearthmetalssuchasGd.χmashighas106,andH<<M:B≈μ0M(4.8)Permanentmagneticmomentsresultfromatomicmagneticmomentsduetouncancelledelectronspinsandasmallerorbitalmagneticmoment.Couplinginteractionscausenetspinmagneticmomentsofadjacentatomstoalignwithoneanother,evenintheabsenceofanexternalfield.MutualalignmentofatomicdipolesforaferromagneticmaterialDomain(磁畴):Mutualspinalignmentexistsoverrelativelylarge-volumeregionsofthecrystal.Saturationmagnetization(饱和磁化强度)Ms:

Themaximumpossiblemagnetization.Thereisalsoacorrespondingsaturationfluxdensity(饱和磁通密度)

Bs.第10页，课件共20页，创作于2023年2月4.4ANTIFERROMAGNETISMANDFERRIMAGNETISMAntiferromagnetism(反铁磁性)Thealignmentofthespinmomentsofneighboringatomsorionsinexactlyoppositedirections;Reason:Magneticmomentcouplingbetweenadjacentatomsorionsresultsinanantiparallelalignment;Thesolidasawholepossessesnonetmagneticmoment.AntiparallelalignmentofspinmagneticmomentsforantiferromagneticMnO第11页，课件共20页，创作于2023年2月Ferrimagnetism(亚铁磁性/铁氧体磁性)Thereareantiparallelspin-couplinginteractions,similarincharactertoantiferromagnetism.Thenetferrimagneticmomentarisesfromtheincompletecancellationofspinmoments.Thesaturationmagnetizationsforferrimagneticmaterialsarenotashighasforferromagnets.Ferrite(铁氧体)inthemagneticsenseshouldnotbeconfusedwiththeferrite(铁素体)α-iron.Ferrites,beingceramicmaterials,aregoodelectricalinsulators.Forsomemagneticapplications,suchashigh-frequencytransformers,alowelectricalconductivityismostdesirable.SpinmagneticmomentconfigurationforFe2+andFe3+ionsinFe3O4第12页，课件共20页，创作于2023年2月4.5THEINFLUENCEOFTEMPERATUREONMAGNETICBEHAVIORRaisingthetemperatureresultsinanincreaseinthemagnitudeofthethermalvibrationsofatoms.Withrisingtemperature,theincreasedthermalmotionoftheatomstendstorandomizethedirectionsofanymoments.Thesaturationmagnetizationisamaximumat0K.Withincreasingtemperature,thesaturationmagnetizationdiminishesgraduallyandthenabruptlydropstozeroattheCurietemperature(居里温度)Tc.FortemperaturesaboveTc,bothferromagneticandferrimagneticmaterialsareparamagnetic.Antiferromagnetismisalsoaffectedbytemperature;thisbehaviorvanishesattheNéeltemperature(尼尔温度).Attemperaturesabovethispoint,antiferromagneticmaterialsalsobecomeparamagnetic.SaturationmagnetizationasafunctionoftemperatureforFeandFe3O4第13页，课件共20页，创作于2023年2月4.6DOMAINSANDHYSTERESISEachdomainismagnetizedtoitssaturationmagnetization;Adjacentdomainsareseparatedbydomainboundariesorwalls,acrosswhichthedirectionofmagnetizationgraduallychanges;Normally,domainsaremicroscopicinsize,andforapolycrystallinespecimen,eachgrainmayconsistofmorethanasingledomain;ThemagnitudeoftheMfieldfortheentiresolidisthevectorsumofthemagnetizationsofallthedomains;Foranunmagnetizedspecimen,thevectorsumofthemagnetizationsofallthedomainsiszero.DomainsinaferromagneticorferrimagneticmaterialThegradualchangeinmagneticdipoleorientationacrossadomainwall第14页，课件共20页，创作于2023年2月FluxdensityBandfieldintensityHarenotproportionalforferromagnetsandferrimagnets.Initialpermeability(初始磁导率)μi:TheslopeoftheB-HcurveatH=0.Hysteresis(磁滞现象):TheBfieldlagsbehindtheappliedHfield.Remanence/remanentfluxdensity(剩磁)Br:ResidualBfieldexistsatzeroHfield.Hysteresisbehaviorandpermanentmagnetizationmaybeexplainedbythemotionofdomainwalls.Coercivity/Coerciveforce(矫顽力)Hc:,A

fieldappliedinadirectionoppositetotheoriginalfieldtoreducetheBfieldtozero.TheB-HbehaviorforaferromagneticorferrimagneticmaterialthatwasinitiallyunmagnetizedTheB-Hbehaviorforaferromagneticmaterialthatissubjectedtoforwardandreversesaturations第15页，课件共20页，创作于2023年2月ItisnotnecessarytoincreasetheHfieldtosaturationbeforereversingthefielddirection.Itispossibletoreversethedirectionofthefieldatanypointalongthecurveandgenerateotherhysteresisloops.DifferenthysteresiscurvesB-Hbehaviorsforferromagnetic/ferromagneticanddiamagnetic/paramagneticmaterialsThebehaviorofatypicalferromagnetic/ferrimagneticmaterialsisnonlinear,andthatofparamagneticanddiamagneticislinear.Paramagneticsanddiamagneticsarenonmagneticmaterials:thefluxdensityBoftheparamagneticanddiamagneticmaterialsitisontheorderof10-5tesla.第16页，课件共20页，创作于2023年2月4.7MAGNETICANISOTROPYThemagnetichysteresiscurveshavedifferentshapesdependingonvariousfactors:(1)asinglecrystalorpolycrystalline;(2)ifpolycrystalline,anypreferredorientationofthegrains;(3)poresorsecond-phaseparticles;and(4)otherfactors,suchastemperatureandthestressstate.Magnetic(ormagnetocrystalline)anisotropy(磁/磁晶各向异性):Thedependenceofmagneticbehavioroncrystallographicorientation.Easymagnetizationdirection(易磁化方向):Acrystallographicdirectioninwhichmagnetizationiseasiest—thatis,saturation(ofM)isachievedatthelowestHfield.MagnetizationcurvesforsinglecrystalsofcobaltMagnetizationcurvesforsinglecrystalsofironandnickel第17页，课件共20页，创作于2023年2月4.8SOFTMAGNETICMATERIALSSoftmagneticmaterials(软磁材料)：Smallhysteresisloop(thinandnarrow)HighinitialpermeabilityandalowcoercivityReachsaturationmagnetizationwitharelativelylowappliedfield(i.e.,iseasilymagnetizedanddemagnetized)LowhysteresisenergylossesSchematicmagnetizationcurvesforsoftandhardmagneticmaterialsThesaturationfieldormagnetizationisdeterminedonlybythecompositionofthematerial.Thesusceptibilityandcoercivity,whichinfluencetheshapeofthehysteresiscurve,aresensitivetostructuralvariablesratherthantocomposition.Eddycurrents(涡流):

Electricalcurrentsinducedinamagneticmaterialbyamagneticfieldthatvariesinmagnitudeanddir