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industrialimpactoftheGMRandrelatedspinelectronicseffectsispresentedinSection6.Finally,theCurriculumVitaeofAlbertFertandPeterGrünbergaregivenintwoAppendices.2.TheGMReffectThemagnetoresistanceisthechangeofelectricalresistanceofaconductorwhensubjectedtoanexternalmagneticfield.Inbulkferromagneticconductors,theleadingcontributiontothemagnetoresistanceisduetotheanisotropicmagnetoresistance(AMR)discoveredin1857byW.Thomson(LordKelvin)(Proc.R.Soc.LondonA8,546(1857)).Thisoriginatesfromthespin-orbitinteraction,whichleadstoadifferentelectricalresistivityforacurrentdirectionparallelorperpendiculartothemagnetizationdirection.Asamagneticfieldisapplied,misorientedmagneticdomainstendtoaligntheirmagnetizationalongthefielddirection,givingrisetoaresistancechangeoftheorderofafewpercent.Magnetoresistiveeffectsareofgreatinterestforindustrialapplications,andtheAMRhasbeenappliedformakingmagneticsensorsandread-outheadsformagneticdisks.Until1988,the130yearsoldAMRremainedthemostimportantcontributiontothemagnetoresistanceofferromagnets.Thesituationatthattimeisbestsummarizedbythefollowingpessimisticquotation,takenfromanauthorativetreatiseonmagneticsensortechnologywrittenin1988:“Morethantwodecadesofresearchanddevelopmenthaveestablishedtheprincipleofmagnetoresistivesensors.(...).Itisdoubtful,however,whethermagnetoresistivelayersthemselveswillbeimprovedconsiderablyinthecomingyears.”(From“Sensors,AComprehensiveSurvey,Vol.5:MagneticSensors”,VCH(1989)).Itwasthereforeagreatsensationwhen,in1988,AlbertFertandPeterGrünbergindependentlydiscoveredthatamuchgreatermagnetoresistiveeffect(hencedubbed“giantmagnetoresistance”orGMR)canbeobtainedinmagneticmultilayers.Thesesystemsessentiallyconsistofanalternatestackofferromagnetic(e.g.,Fe,Co,Ni,andtheiralloys)andnon-ferromagnetic(e.g.,Cr,Cu,Ru,etc.)metalliclayers.Eachindividuallayerinthesemultilayersisonlyafewatomiclayersthick.FertandGrünbergdiscoveredthatwhentherelativeorientationofthemagnetizationofthesuccessiveferromagneticlayersischangedfromantiparalleltoparallelbyapplyinganexternalmagneticfield,theelectricalresistanceofthemultilayersisreducedbyasmuchas50%asshownschematicallyinFigure1.Page2of18October2002Fig.1.Schematicdescriptionofthegiantmagnetoresistanceeffect.Bluecurve:magnetizationofthemultilayerversusappliedmagneticfield.Redcurve:electricalresistanceofthemultilayer.Theinsetsindicatethemagneticconfigurationofthemultilayerinzerofieldandatpositiveandnegativesaturationfields.ThephenomenonofGMRresultsfromacombinationoftwophysicallydistinctneweffects.Thefirstoneistheveryfactthattheelectricalresistanceofthemultilayervariesconsiderablyastheconfigurationisswitchedfromparallel(P)toantiparallel(AP).Thiseffectarisesasaconsequenceofthespin-dependentscatteringofelectronsinferromagneticlayers,whichinthe70’shasbeenintensivelystudiedbyAlbertFertinbulkferromagnetsandferromagneticalloys.ThiseffectisshownschematicallyinFigure2.Thesecondimportantneweffectistheantiferromagneticinterlayerexchangecoupling(discoveredbyPeterGrünbergin1986),whichleadstoanantiparallelorientationofthemagnetizationsofsuccessiveferromagneticlayersinabsenceofanexternalfield;thiseffectallowsone(byapplyinganexternalmagneticfield)toeffectivelyswitchfromtheAPconfigurationtothePconfiguration,andthustorevealtheGMRphenomenon.Page3of18October2002Fig.2.Schematicdescriptionofthespin-dependentscatteringmechanismforthegiantmagnetoresistance.Electronsarestronglyscatteredinmagneticlayerswithmagnetizations(whitearrows)antiparalleltotheirspin(blackarrows),andweaklyscatteredinmagneticlayerswithmagnetizationsparalleltotheirspin.Thisresultsinashort-circuiteffectinthePconfiguration,wherehalfoftheelectronsareseldomscattered,yieldingalowernetresistance.TheGMRhasoriginallybeendiscoveredinthe“current-in-plane”(CIP)configuration,whichistheeasiesttostudyexperimentally.Later,itwasshownthatanevenlargereffecttakesplaceinthe“current-perpendicular-to-plane”(CPP)configuration.3.ScientificcontributionsofAlbertFertLongbeforethediscoveryofgiantmagnetoresistance,thestudyofspin-polarizedelectronictransportinmagneticmaterialshasbeenamajorresearchtopicofAlbertFert.Inthe70’s,togetherwithI.A.Campbell,heperformedpioneeringstudiesontheresistivityofferromagneticalloys(Phys.Rev.Lett.21,1190(1968)∗;J.dePhysiqueC1-32,1(1971);J.Phys.F6,849(1976)).Inthesestudies,hedevelopedtheconceptsofspin-dependentcurrents(originallysuggestedbyMott),ofspin-dependentresistivityandspin-dependentscattering,whichlaterbecamethekeyconceptualingredientsoftheGMReffect.∗Thereferencesmarkedinbluearelinkedviainternettothecorrespondingpaper.Dependingontheonlinesubscriptionofyourinstitution,youmayeitherhaveaccesstothefulltextoronlytotheabstract.Page4of18October2002Inthemid-80’s,AlbertFertstartedworkingonmagneticmultilayers,andhisexperiencewithspin-polarizedtransportinmagneticalloyspromptedhimtofocusontheirelectronictransportproperties.Hesoonrealizedthattheeffectofspin-dependentscatteringwouldgiverisetomagnetoresistanceeffectsofunprecedentedmagnitude,providedonefindsameantoswitchtherelativeorientationofthemagnetizationofs