askelandphulenotes-ch19printable

1TheScienceandEngineeringofMaterials,4thedDonaldR.Askeland–PradeepP.PhuléChapter19–MagneticMaterials2ObjectivesofChapter19Tostudythefundamentalbasisforresponsesofcertainmaterialstothepresenceofmagneticfields.Toexaminethepropertiesandapplicationsofdifferenttypesofmagneticmaterials.3ChapterOutline19.1ClassificationofMagneticMaterials19.2MagneticDipolesandMagneticMoments19.3Magnetization,Permeability,andtheMagneticField19.4Diamagnetic,Paramagnetic,Ferromagnetic,Ferrimagnetic,andSuperparamagneticMaterials19.5DomainStructureandtheHysteresisLoop19.6TheCurieTemperature19.7ApplicationsofMagneticMaterials19.8MetallicandCeramicMagneticMaterials4FerromagnetismFerrimagnetismDiamagnetismAntiferromagnetismHardmagnetSection19.1ClassificationofMagneticMaterials5Themagneticbehaviorofmaterialscanbetracedtothestructureofatoms.Bohrmagneton-Thestrengthofamagneticmomentofanelectron(μB)duetoelectronspin.Section19.2MagneticDipolesandMagneticMoments6©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure19.1Originofmagneticdipoles:(a)Thespinoftheelectronproducesamagneticfieldwithadirectiondependentonthequantumnumberms.(b)ElectronsElectronsorbitingaroundthenucleuscreateamagneticfieldaroundtheatom.78Magneticpermeability-Theratiobetweeninductanceormagnetizationandmagneticfield.Itisameasureoftheeasewithwhichmagneticfluxlinescan‘‘flow’’throughamaterial.Magnetization-Thetotalmagneticmomentperunitvolume.Magneticsusceptibility-Theratiobetweenmagnetizationandtheappliedfield.Section19.3Magnetization,Permeability,andtheMagneticField9©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure19.2AcurrentpassingthroughacoilsetsupamagneticfieldHwithafluxdensityB.Thefluxdensityishigherwhenamagneticcoreisplacedwithinthecoil.1011Calculatethemaximum,orsaturation,magnetizationthatweexpectiniron.ThelatticeparameterofBCCironis2.866Å.Comparethisvaluewith2.1tesla(avalueofsaturationfluxdensityexperimentallyobservedforpureFe.)Example19.1SOLUTIONBasedontheunpairedelectronicspins,weexpecteachironatomtohavefourelectronsthatactasmagneticdipoles.Thenumberofatomsperm3inBCCironis:Example19.1TheoreticalandActualSaturationMagnetizationinFe12Example19.1SOLUTION(Continued)Themaximumvolumemagnetization(Msat)isthetotalmagneticmomentperunitvolume:ToconvertthevalueofsaturationmagnetizationMintosaturationfluxdensityBintesla,weneedthevalueofμ0M.Inferromagneticmaterialsμ0Mμ0Handtherefore,Bμ0M.Saturationinductionintesla=Bsat=μ0Msat.13Section19.4Diamagnetic,Paramagnetic,Ferromagnetic,Ferrimagnetic,andSuperparamagneticMaterialsFerromagnetism-Alignmentofthemagneticmomentsofatomsinthesamedirectionsothatanetmagnetizationremainsafterthemagneticfieldisremoved.Ferrimagnetism-Magneticbehaviorobtainedwhenionsinamaterialhavetheirmagneticmomentsalignedinanantiparallelarrangementsuchthatthemomentsdonotcompletelycanceloutandanetmagnetizationremains.Diamagnetism-Theeffectcausedbythemagneticmomentduetotheorbitingelectrons,whichproducesaslightoppositiontotheimposedmagneticfield.14Section19.4(Continued)Antiferromagnetism-Arrangementofmagneticmomentssuchthatthemagneticmomentsofatomsorionscanceloutcausingzeronetmagnetization.Hardmagnet-Ferromagneticorferrimagneticmaterialthathasacoercivity104A.m-1.15©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure19.3Theeffectofthecorematerialonthefluxdensity.Themagneticmomentopposesthefieldindiamagneticmaterials.Progressivelystrongermomentsarepresentinparamagnetic,ferrimagnetic,andferromagneticmaterialsforthesameappliedfield.16©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure19.4ThecrystalstructureofMn0consistsofalternatinglayersof{111}typeplanesofoxygenandmanganeseions.Themagneticmomentsofthemanganeseionsineveryother(111)planeareoppositelyaligned.Consequently,Mn0isantiferromagnetic.17Wewanttoproduceasolenoidcoilthatproducesaninductanceofatleast2000gausswhena10-mAcurrentflowsthroughtheconductor.Duetospacelimitations,thecoilshouldbecomposedof10turnsovera1cmlength.Selectacorematerialforthecoil.Example19.2Design/MaterialsSelectionforaSolenoid1819Example19.2SOLUTIONThemagneticfieldHproducedbythecoil.Thepermeabilityofthecorematerialmustbe:Therelativepermeabilityofthecorematerialmustbeatleast:FromTable19-4,wefindthat4-79permalloyhasamaximumrelativepermeabilityof80,000andmightbeagoodselectionforthecorematerial.20Domains-Smallregionswithinasingleorpolycrystallinematerialinwhichallofthemagnetizationdirectionsarealigned.Blochwalls-Theboundariesbetweenmagneticdomains.Saturationmagnetization-Whenallofthedipoleshavebeenalignedbythefield,producingthemaximummagnetization.Remanance-Thepolarizationormagnetizationthatremainsinamaterialafterithasbeenremovedfromthefield.Hysteresisloop-Thelooptracedoutbymagnetizationinaferromagneticorferrimagneticmaterialasthemagneticfieldiscycled.Section19.5DomainStructureandtheHysteresisLoop21©2003Brooks/Co