磁性材料补充课外读物

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1、Thehistoryofpermanentmagnetismdatesbackovermanycenturies.TheearliestthobservationsofmagnetismcanbetracedbacktotheGreekphilosopherThalesinthe6CenturyB.C.However,itwasnotuntil1600thatthemodernunderstandingofmagnetismbegan.1600:Dr.WilliamGilbertpublishedthefir

2、stsystematicexperimentsonmagnetismin"DeMagnete".1819:Oersteadaccidentallymadetheconnectionbetweenmagnetismandelectricitydiscoveringthatacurrentcarryingwiredeflectedacompassneedle.1825:Sturgeoninventedtheelectromagnet.1880:Warburgproducedthefirsthysteresislo

3、opforiron.1895:TheCurielawwasproposed.1905:Langevinfirstexplainedthetheoryofdiamagnetismandparamagnetism.1906:Weissproposedferromagnetictheory.1920's:Thephysicsofmagnetismwasdevelopedwiththeoriesinvolvingelectronspinsandexchangeinteractions;thebeginningsofq

4、uantummechanics.Theprogressofpermanentmagneticmaterialsproceedsinaseriesofsteps.Eachmaterialisdevelopedandimprovedbeforebeingsupplantedbyanewone.Thistrendisshowninfigureth1awhichshowsthedevelopmentofpermanentmagnetmaterialsthroughoutthe20century.Thegraphsho

5、wstheimprovementinmaximumenergyproductofthematerials,whichisusedasafigureofmerit,asitisameasureoftheabilityofmagnetstodoworkperunitvolumeofmaterial.Thereductioninsizeofmagnetsisillustratedmorevividlyinfigure1b.Figure1a:Thedevelopmentofpermanentmagnetsinthe2

6、0thCentury.BHmaxhasimprovedexponentially,doublingevery12years.1Figure1b:Brassboundlodestone,ferriteblockandNdFeBmagnet:eachstorethesamemagneticenergy(~0.4J)&contain~70%ironbyweight,yetthemasshasdecreasedathousandfold.Lodestone:Thiswasthefirstpermanentmagnet

7、toberecognised;anaturallyoccurringoxideFe3O4.Lighteningstrikesarethoughttoberesponsibleforthelargemagneticfieldsthatinitiallymagnetisedtherocks.Themagneticfieldproducedislow,however,theresistancetodemagnetisationisreasonablyhigh.MagneticCarbonSteel:Thesewer

8、edevelopedintheeighteenthcentury.Thesesteelsarenormallyalloyedwithtungstenand/orchromiumtoformcarbideprecipitatesunderappropriateheattreatments,whichareeffectiveinobstructingdomainwallmovement.Thesemag