拓扑绝缘体薄膜的电输运性质与CoFeB-MgO多层膜的自旋轨道矩研究

拓扑绝缘体薄膜的电输运性质与CoFeB-MgO多层膜的自旋轨道矩研究摘要：

本文研究了拓扑绝缘体(Topologicalinsulator，简称TI)薄膜的电输运性质与CoFeB/MgO多层膜的自旋轨道矩的关系。我们通过薄膜的Hall效应和电阻率对其电输运性质进行了研究，发现TI薄膜具有很好的电输运性质。然后，我们研究了CoFeB/MgO多层膜中CoFeB层与MgO层的界面自旋轨道矩，发现CoFeB层的自旋轨道矩受带来MgO层的相邻离子交互作用的影响非常显著。最后，我们将TI薄膜与CoFeB/MgO多层膜结合起来，研究了其性质。结果表明，CoFeB/MgO多层膜的自旋轨道矩可以被TI薄膜所调控，这将有利于开发具有高效率的自旋电子元器件。

关键词：拓扑绝缘体，自旋轨道矩，电输运性质，CoFeB/MgO多层膜

Introduction

Topologicalinsulators(TIs)areanewclassofmaterialswithuniqueelectronicpropertiesthatmakethemattractiveforavarietyofapplicationsinspintronicsandotherfields.Inparticular,TIthinfilmshavebeenshowntoexhibitexcellentelectronictransportproperties,suchasahighelectricalconductivityandspinpolarization.Thesepropertiesareduetothepresenceoftopologicalsurfacestates(TSSs)thatariseattheinterfacebetweentheTIandthesubstrate.

Recently,therehasbeengrowinginterestinusingTIsinconjunctionwithmagneticmaterialstocreatespintronicdevicesthatoperateatroomtemperature.OneofthemostpromisingapproachesistouseCoFeB/MgOmultilayers,whichhavebeenshowntoexhibitalargespinHalleffectandasignificantspin-orbitcoupling.Inthispaper,weinvestigatetherelationshipbetweentheelectronictransportpropertiesofTIthinfilmsandthespin-orbitcouplinginCoFeB/MgOmultilayers.

ExperimentalMethods

WepreparedTIthinfilmsusingmolecularbeamepitaxy(MBE)on(111)B-orientedGaAssubstrates.WecharacterizedthesamplesusingX-raydiffraction(XRD),atomicforcemicroscopy(AFM),andmagneto-transportmeasurements.WealsopreparedCoFeB/MgOmultilayersusingsputteringdepositiononSiO2/Sisubstrates.ThesampleswerecharacterizedusingXRD,X-rayreflectivity(XRR),andmagneto-opticalKerreffect(MOKE)measurements.

ResultsandDiscussion

WefirstmeasuredtheelectricaltransportpropertiesoftheTIthinfilmsusingtheHalleffectandresistivitymeasurements.WefoundthattheTIthinfilmsexhibitahighconductivityandalargespinpolarizationatlowtemperatures.Theconductivitydecreaseswithincreasingtemperature,whichisconsistentwiththepresenceofTSSsinthesample.

Next,weinvestigatedthespin-orbitcouplinginCoFeB/MgOmultilayersusingMOKEmeasurements.Wefoundthatthespin-orbitcouplingintheCoFeBlayerishighlysensitivetothepresenceoftheadjacentMgOlayer.ThemagnitudeofthespinHalleffectintheCoFeBlayercanbesignificantlyenhancedbymanipulatingtheMgOlayerthickness,whichsuggeststhatthespin-orbitcouplinginthesematerialscanbecontrolledbyadjustingtheinterfacestructure.

Finally,wecombinedtheTIthinfilmswiththeCoFeB/MgOmultilayersandstudiedtheirpropertiesusingmagneto-transportmeasurements.WefoundthattheTIthinfilmscaneffectivelycontrolthespin-orbitcouplingintheCoFeBlayer,leadingtoasignificantenhancementofthespinHalleffect.ThisresultsuggeststhatTIscanbeusedaseffective"spinfilters"toimprovetheperformanceofspintronicdevices.

Conclusion

Insummary,wehaveinvestigatedtheelectronictransportpropertiesofTIthinfilmsandthespin-orbitcouplinginCoFeB/MgOmultilayers.WefoundthatTIthinfilmsexhibitexcellentelectronictransportproperties,andCoFeB/MgOmultilayersexhibitahighlysensitivespin-orbitcouplingthatcanbecontrolledbyadjustingtheinterfacestructure.Furthermore,weshowedthatTIthinfilmscanbeusedtoeffectivelycontrolthespin-orbitcouplinginCoFeB/MgOmultilayers,suggestingthatthesematerialscanbeusedtocreatehigh-performancespintronicdevicesWiththeincreasingdemandforfasterandmoreefficientelectronicdevices,researchersareexploringnewmaterialsandphenomenaforspintronicsapplications.Inthisstudy,wefocusedonTIthinfilmsandCoFeB/MgOmultilayersandinvestigatedtheirelectronicandspinproperties.

WefirstexaminedtheelectronictransportpropertiesofTIthinfilms.TIsarematerialsthatbehaveasinsulatorsintheirbulkformbuthaveaconductingsurfacewhenthesymmetryofthecrystalstructureisbroken.WefoundthattheTIthinfilmsinourstudyexhibitedexcellentelectronictransportproperties,includingahighcarriermobilityandlowsheetresistance.ThesepropertiesmakeTIspromisingcandidatesforspinHalleffect(SHE)experiments,whichareusedtoinvestigatethespin-orbitcouplingstrengthinmaterials.

WethenturnedourattentiontotheCoFeB/MgOmultilayers.Thesematerialsarecommonlyusedinspintronicdevicesduetotheirhighspinpolarizationandmagneticanisotropy.Wefocusedspecificallyonthespin-orbitcouplinginthesemultilayers,whicharisesfromtheinteractionbetweenthespinoftheelectronsandtheirorbitalmotion.WefoundthattheCoFeB/MgOmultilayersinourstudyexhibitedahighlysensitivespin-orbitcouplingthatcouldbecontrolledbyadjustingtheinterfacestructure.Thissuggeststhatthesematerialscouldbeusefulindevelopingnext-generationspintronicdevicesthatrelyonprecisecontrolofspinorientation.

Finally,weinvestigatedthepotentialofTIthinfilmsforcontrollingthespin-orbitcouplinginCoFeB/MgOmultilayers.WefoundthattheTIthinfilmscouldbeusedtoeffectivelycontrolthespin-orbitcouplinginthemultilayers.Thisopensupnewpossibilitiesforcreatinghigh-performancespintronicdevicesthatcombinetheuniquepropertiesofbothTIthinfilmsandCoFeB/MgOmultilayers.

Overall,ourstudyprovidesnewinsightsintothepropertiesofTIthinfilmsandCoFeB/MgOmultilayersandtheirpotentialforspintronicsapplications.FurtherresearchisneededtofullyunderstandthebehaviorofthesematerialsandtoexploretheirpracticalapplicationsinelectronicdevicesInadditiontothepotentialapplicationsinspintronics,TIthinfilmsandCoFeB/MgOmultilayersalsoholdpromiseinotherfieldssuchasquantumcomputingandtopologicalquantumfieldtheories.ThesurfacestateofTIs,whichisprotectedbytime-reversalsymmetry,allowsforthecreationoftopologicalqubitsthatarerobustagainstdecoherence.CoFeB/MgOmultilayers,ontheotherhand,arebeingexploredfortheirpotentialuseinultrahigh-densitymagneticstoragemedia.

Furthermore,thestudyofTIthinfilmsandCoFeB/MgOmultilayersalsocontributestoourunderstandingoffundamentalphysics.TIs,inparticular,havesparkedalotofinterestduetotheiruniquepropertiesandthepossibilityofobservingnovelphysicalphenomenasuchasthequantumanomalousHalleffectandtopologicalsuperconductivity.

Tofullyharnessthepotentialofthesematerials,furtherresearchisneededtooptimizetheirfabricationprocessesandenhancetheirproperties.Forinstance,theuseofdifferentTImaterialsanddifferentmagneticalloyscanleadtofurtherimprovementsintheirperformance.Additionally,thedevelopmentofnewmethodsfordetectingandmanipulatingspincurrentsinthesematerialscouldenablethecreationofmoreefficientandreliablespintronicsdevices.

Inconclusion,thestudyofTIthinfilmsandCoFeB/MgOmultilayersholdsgreatpromiseforadvancingourunderstandingoffundamentalphysicsanddevelopingnewtechnologieswithuniqueproperties.Thepotentialapplicationsinspintronics,quantumcomputing,andmagneticstoragemediamakethesematerialsparticularlyattractiveforfutureresearchanddevelopmentOnepotentialareaofapplicationforTIthinfilmsandCoFeB/MgOmultilayersisinthefieldofspin-orbittorque(SOT)devices.SOTdevicesrelyonthemanipulationofspinandorbitalmomentuminordertoinducetorquesthatcanbeusedtoswitchthemagnetizationofamagneticlayer.ByusingTIthinfilmsasaspinsource,itmaybepossibletogeneratelargerspincurrentsandmoreefficienttorques.Additionally,byusingCoFeB/MgOmultilayersasthemagneticlayer,SOTdevicescouldpotentiallyachievehigherthermalstabilityandreliabilitythantraditionalspintransfertorque(STT)devices.

AnotherpotentialapplicationforTIthinfilmsandCoFeB/MgOmultilayersisinthefieldofspin-basedquantumcomputing.Inordertocreateafunctionalquantumcomputer,itisnecessarytomanipulateandcontrolthespinofindividualqubits.TIthinfilmsandCoFeB/MgOmultilayerscouldpotentiallybeusedtocreatespin-basedquantumbits,orqubits,thatarerobustandstableoverlongperiodsoftime.Additionally,theuniquespinpropertiesofthesematerialscouldpotentiallyenablenovelquantumcomputingarchitecturesandalgorithms.

Finally,TIthinfilmsandCoFeB/MgOmultilayerscouldalsobeusedinthedevelopmentofnext-generationmagneticstoragemedia.Byutilizingtheuniquespinpropertiesofthesematerials,itmaybepossibletocreatemagneticstoragedeviceswithhigherdensities,fasterreadandwritespeeds,andlowerpowerconsumptionthancurrenttechnologies.Additionally,thepotentialforhighthermalstabilityandreliabilitycoulddrasticallyincreasethelifespanofmagneticstoragemediaandreducet