材料物理性能-lecture1-磁性.

材料科学与工程导论-IIPhysicalPropertiesandFunctionalMaterials（材料物理性能和功能材料）ZhongwuLiu（刘仲武）Webpage:@scut.edu.cnTel:22236906Office:Rm.82172Courseintroduction•12hours•4lectures(3hourseach)•Magneticpropertiesandmagneticmaterials•Electricpropertiesandelectricmaterials•Thermalproperties•Opticalproperties•1/3inexam3Aboutyourreport(课程论文):mustinformalpaperstyle题目作者，学号，指导老师地址（院系，通讯地址）Abstract(英文摘要)中文摘要关键词正文1.2.…参考文献(统一格式)4PropertiesofMaterials•Mechanicalpropertiesstructuralmaterials•Chemicalproperties•Physicalpropertiesfunctionalmaterials•Magneticproperties•Thermalconductivity•Electricalconductivity,Insulatingproperties•Opticalproperties•AcousticpropertiesPhysicalPropertiesandFunctionalMaterialsPart1MagneticPropertiesandMagneticMaterials（材料的磁性能和磁性材料）6Outline•Preface•Basicconceptsofmagnetism•Fundamentalmagnetism•Permanentmagneticmaterials•Softmagneticmaterials•Magneticrecording•Othermagneticmaterials•Magneticmeasurements7•TermMagnetcomesfromtheancientGreekcityofMagnesia,atwhichmanynaturalmagnetswerefound.•PlinytheElder(23-79ADRoman)wroteofahillneartheriverIndusthatwasmadeentirelyofastonethatattractediron.•KnowninChinaandEurope-800BCLodestoneLet’sgetstart:Astory8Lodestone•Now,werefertothesenaturalmagnetsaslodestones(alsospelledloadstone;lodemeanstoleadortoattract)whichcontainmagnetite,anaturalmagneticmaterialFe3O4.•Whenlightningstrikestheearthitcouldcreateamagneticfieldlargeenoughtosaturatethemagnetizationoflodestone.Typicalcurrent~1,000,000Amp.Oncein1–10millionyears9HistoryChineseasearlyas121ADknewthatanironrodwhichhadbeenbroughtnearoneofthesenaturalmagnetswouldacquireandretainthemagneticproperty…andthatsucharodwhensuspendedfromastringwouldalignitselfinanorth-southdirection.Useofmagnetstoaidinnavigationcanbetracedbacktoatleastthe11thcentury.Basically,weknewthephenomenonexistedandwelearnedusefulapplicationsforit.Wedidnotunderstandit.司南10ElectrifiedAmberattractssmallobjectsLodestoneattractsironAConnection?HansChristianØrsted(1777–1851)Finally,theScience-Oersted’sExperiment•DanishscientistHansChristianOersted（奥斯特）observedthatacompassneedleinthevicinityofawirecarryingelectricalcurrentwasdeflected!•aconnectionbetweenelectricalandmagneticphenomenashown.Oersted’sexperiment(1820)11AquantitativerelationshipbetweenachangingmagneticfieldandtheelectricfieldcreatedbythechangeMichaelFaraday(1791-1867)Faraday:Effectofachangingmagneticfield•In1831,Faraday（法拉第）discoveredthatamomentarycurrentexistedinacircuit,whenthecurrentinanearbycircuitwasstartedorstopped.•Shortlythereafter,hediscoveredthatmotionofamagnettowardorawayfromacircuitcouldproducethesameeffect.12Henry’swork:alesson!JosephHenry(1797-1878)•JosephHenryfailedtopublishwhathehaddiscovered6-12monthsbeforeFaraday•Henrywasalwaysslowinpublishinghisresults,andhewasunawareofFaraday'swork.•TodayFaradayisrecognizedasthediscovererofmutualinductance(thebasisoftransformers),whileHenryiscreditedwiththediscoveryofself-inductance.13MagneticDipoles（磁偶极子）NSAmagneticdipoleiscomposedof2magnetic“charges”orpoles,1northpoleand1southpole.Themagneticfieldofthemagneticdipolelooksidenticaltotheelectricdipole（电偶极子）.EBAtomscanexhibitmagneticpropertiesthatsometimesmimicthissimplebarmagnetbehavior.Thisgivesbulkmaterialsmagneticbehavior.Basicconcepts（磁学基本概念）14BasicconceptsMagneticfieldH（磁场,A/m）•Aforcefieldsimilartothegravitationalandelectricalfield,detectedbyaprobe.•Amagneticfieldexertsatorquewhichorientsdipoleswiththefield.•Directionofmagneticfieldatanypointisdefinedasthedirectionofmotionofachargedparticleonwhichthemagneticfieldwouldnotexertaforce.•Magneticfieldlinesdescribethestructureofmagneticfieldsinthreedimensions.MagneticfieldstrengthHForamagnetriH2NiH2221211rmkrmmkmmFHm1m2r15BasicconceptsMagneticmoment（磁矩）AmagneticmomentM(Am2)generatedbyacyclecurrent.M=IA=M=iπr2Themomentproducedbyncycles:M=niπr2Magneticmomentforabarmagnet:M=mlStaticmagneticenergyMagnetostaticenergy:E=-MBlmA(m2)I(A)m16OriginofMagnetismofMatter•Ampere:molecularcurrents（“分子电流学说”）•Modernphysics:magneticmomentsinatoms（“磁矩学说”）NAmperefirstsuggestedin1820thatmagneticpropertiesofmatterwereduetotinyatomiccurrents:Existenceofsmallmolecularcurrents；Eachatom/moleculewouldbehaveasasmallpermanentmagnetAndreMarieAmpere(1775-1836)1)Nucleusmagneticmoment2)Electronicorbitalmagneticmoment3)Electronicspinmagneticmoment17OriginofMagnetismofMatterMagneticmomentofanatom（原子磁矩）:1)Nucleusmagneticmoment2)Electronicorbitalmagneticmoment3)ElectronicspinmagneticmomentThenetmagneticmomentforanatomisthesumofthemagneticmomentsofconstituentelectronsandnucleus.Thenetmagneticmomentforamaterialisthesumofthemagneticmomentsofconstituentatoms.成对的电子由于自旋方向相反，自旋磁矩和轨道磁矩各自互相抵消。18•原子核的磁矩仅有电子磁矩的1/1836.5。•Electronicorbitalmagneticmoment(电子轨道磁矩)：l：轨道角量子数,波尔磁子B=9.273210-24A/m2轨道磁矩在外磁场方向的投影:l,H=mlBml:角动量方向量子数或磁量子数=0,1,2,…l•Electronicspinmagneticmoment(电子自旋磁矩)：s：自旋量子数，s=1/2;ms:自旋角动量方向量子数=1/2自旋磁矩在外磁场方向的投影:s,H=2msB=BMagneticmomentofanatomBllmcehl4BSsmcehs22只需考虑未填满壳层的电子！19Recall:四个量子数•主量子数n，角量子数l和磁量子数ml确定电于在空间运动的轨道，