ApplPhysLett_88_062502

额外热舞

Combining half-metals and multiferroics into epitaxial heterostructures forspintronics

H. Béa, M. Bibes, M. Sirena, G. Herranz, K. Bouzehouane et al.

Citation: Appl. Phys. Lett. 88, 062502 (2006); doi: 10.1063/1.2170432

View online: http://wendang.chazidian.com/10.1063/1.2170432

View Table of Contents: http://wendang.chazidian.com/resource/1/APPLAB/v88/i6

Published by the American Institute of Physics.

Additional information on Appl. Phys. Lett.

Journal Homepage: http://wendang.chazidian.com/

Journal Information: http://wendang.chazidian.com/about/about_the_journal

Top downloads: http://wendang.chazidian.com/features/most_downloaded

Information for Authors: http://wendang.chazidian.com/authors

Downloaded 08 Apr 2013 to 219.228.57.28. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://wendang.chazidian.com/about/rights_and_permissions

额外热舞

APPLIEDPHYSICSLETTERS88,062502?2006?

Combininghalf-metalsandmultiferroicsintoepitaxialheterostructuresforspintronics

H.Béa

UnitéMixtedePhysiqueCNRS-Thales,RouteDépartementale128,91767Palaiseau,France

M.Bibesa?

Institutd’ElectroniqueFondamentale,UniversitéParis-Sud,91405Orsay,France

M.Sirena,G.Herranz,K.Bouzehouane,andE.Jacquet

UnitéMixtedePhysiqueCNRS-Thales,RouteDépartementale128,91767Palaiseau,France

S.Fusil

Universitéd’Evry,BâtimentdesSciences,ruedupèreJarlan,91025Evry,France

P.ParuchandM.Dawber

DPMC,UniversityofGeneva,24QuaiE.Ansermet,1211Geneva4,Switzerland

J.-P.ContourandA.Barthélémy

UnitéMixtedePhysiqueCNRS-Thales,RouteDépartementale128,91767Palaiseau,France

?Received4August2005;accepted9December2005;publishedonline6February2006?WereportonthegrowthofepitaxialbilayersoftheLa2/3Sr1/3MnO3?LSMO?half-metallicferromagnetandtheBiFeO3?BFO?multiferroic,onSrTiO3?001?bypulsedlaserdeposition.Thegrowthmodeofbothlayersistwodimensional,whichresultsinunit-cellsmoothsurfaces.Weshowthatbothmaterialskeeptheirpropertiesinsidetheheterostructures,i.e.,theLSMOlayer?11nmthick?isferromagneticwithaCurietemperatureof?330K,whiletheBFO?lmsshowsferroelectricitydowntoverylowthicknesses?5nm?.Conductive-tipatomicforcemicroscopemappingsofBFO/LSMObilayersfordifferentBFOthicknessesrevealahighandhomogeneousresistivestatefortheBFO?lmthatcanthusbeusedasaferroelectrictunnelbarrierintunneljunctionsbasedonahalf-metal.©2006AmericanInstituteofPhysics.?DOI:10.1063/1.2170432?

Toagreatextent,today’sresearchinspintronicsfocusesonthedevelopmentofmaterialsanddevicesconcepts.1Inmanycases,theformerarerequisitestothelatter.Recently,severalfamiliesofmaterialshavebeendevelopedinthissense,atypicalexamplebeingthatofdilutedmagneticsemiconductors.2Asspintronicseffectsrelyonthespinpolarizationoftheelectricalcurrent,materialswithlarge,ideallytotal,spin-polarizationhavealsobeenextensivelyinvestigated.Withtheseso-calledhalf-metals,3aconsider-ableincreaseinthetunnelmagnetoresistanceofmagnetictunneljunctions4hasindeedbeenachieved,atleastatlowtemperatures.5

Anotheremergingfamilyofmagneticmaterialsaremultiferroics.6Inthesecompounds,severalferroicorders?e.g.,magneticandelectric?coexist,withsomecouplingbetweenthem?themagnetoelectriceffect?.7Mostareferroelectricandantiferromagnetic,anotableexceptionbeingBiMnO3thatisferromagnetic.8ApropotypicalmultiferroicthathasattractedalotofattentionlatelyisBiFeO3?BFO?.9,10Itisaferroelectricandweaklyferromagneticrhombohedralperovskitewithordertem-peraturesfaraboveroomtemperature?TC=1043K,11TN=647K?.12BFOthuscrystallizesinthesamestructureasseveralknownhalf-metallicferromagnets?suchasLa2/3Sr1/3MnO3,La2/3Ca1/3MnO3,orSr2FeMoO6?,whichmakesitpossibletocombineitwiththesematerialsinmul-tifunctionalepitaxialheterostructures.Severalpromisingtypesofdevicescanbeimaginedfromthiscombination,as

a?

Electronicmail:manuel.bibes@ief.u-psud.fr

discussed,forinstance,byBineketal.13,14Inparticular,onecanthinkofusingverythinlayersofBiFeO3asmultiferroictunnelbarriers.Ifferroelectric,theselayersshouldhavethesamefunctionalitiesasthoseofrecentlydeveloped15andmodeled16,17ferroelectrictunnelbarriers,combinedwithamagneticorderingandapossiblemagnetoelectriccoupling.

Inthisletter,wedescribethegrowthandpropertiesofbilayersoftheLa2/3Sr1/3MnO3?LSMO?half-metalcombinedwithBFOandepitaxiallygrownontoSrTiO3?001?substratesbypulsedlaserdeposition.Westudythemorphological,structural,electrical,andmagneticpropertiesofBFO/LSMObilayers.WeshowthatthemagneticpropertiesofLSMOarepreservedandthattheBFOlayersareinsulatingandferro-electric,downtothicknessesoftBFO=5nm.BFOultrathinlayersthusful?llsomeimportantcriteriaforbeingusedasferroelectrictunnelbarriers.

ThesamplesusedinthisstudyhavebeengrownbypulsedlaserdepositionusingaNd:yttrium–aluminium–garnet?YAG?laser,atafrequencyof2.5Hz.TheLSMOtargetwasstoichiometricwhileforBFO,atargetwithnomi-nalcompositionBi1.15FeO3wasused,inordertocompensateforthehighvolatilityofBi.?001?-orientedSrTiO3?STO?substrateswereused.Inthepseudo-cubicrepresentation,BFOhasaunit-cellparameterof3.96Å,LSMOof3.88Å,andSTOof3.905Å,sothattheSTOsubstrateinducesatensilestrainonLSMOandacompressivestrainonBFO.TheoptimalgrowthconditionsforLSMOwerepreviouslydeterminedtobeofadepositiontemperatureTdep=720°CandanoxygenpressureofPdep=0.41mbar,18withapostan-nealingat300mbarofO2.Werecentlydeterminedthe

©2006AmericanInstituteofPhysics

0003-6951/2006/88?6?/062502/3/$23.0088,062502-1

Downloaded 08 Apr 2013 to 219.228.57.28. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://wendang.chazidian.com/about/rights_and_permissions

额外热舞

062502-2Beaetal.Appl.Phys.Lett.88,062502?2006?

FIG.2.?a?MagnetichysteresisloopsoftheBFO/LSMO//STObilayerwithtBFO=5nmmeasuredbySQUIDat10K.?b?Temperaturedependenceofthemagnetizationina?eldof1kOe,normalizedtothemagnetizationat10K?M10K?forthesamesample.

FIG.1.RHEEDpatternsinthe?100?directionofthesamplewithtBFO=20nm?a?oftheSTOsubstratebeforedeposition,?b?afterdepositionoftheLSMOlayer,and?c?afterdepositionoftheBFO.Thepatternismorediffusein?b?becausethepressureofmeasurementwas6?10?3mbarcom-paredto10?6mbarfor?a?and?c?.?d?X-raydiffractionspectraofBFO/LSMO//STObilayerswithtLSMO=11nmandtBFO=5nmand70nm.S,L,andBlabelpeaksofSTO,LSMO,andBFO,respectively.?e?RSMofthe?103?re?ectionsoftheBFO?70nm?/LSMO//STObilayer;r.l.u.isforre-ciprocalspace

units.

Pdep-TdepphasestabilitydiagramforBFO?lmsandfoundthatoptimalconditionsarearoundTdep=580°CandPdep=6?10?3mbar.19Inthepresentsamples,theLSMOlayer?11nmthickforallsamples?wasgrown?rst,andtheBFO?lm?tBFO=1–70nm?afterward.Tolimitapossibledeoxygenationofthemanganite,afterthegrowthoftheLSMO?lm,thepressurewaskeptattheLSMOdepositionpressurewhiledecreasingTdepto580°C.Then,thepressurewasrapidlydecreasedto6?10?3mbar,togrowtheBFOlayer.Thesamplewas?nallycooledtoroomtemperaturein300mbarofoxygen.

Re?ectionhigh-energyelectrondiffraction?RHEED?patternswerecollected?atanaccelerationvoltageof25kV?beforegrowth,andafterdepositingeachlayer.Imagesforthe?100?directionareshowninFigs.1?a?–1?c?,andindicateatwo-dimensionalgrowthfortheLSMOandtheBFOlayer?uptoatleasttBFO=35nm?.Anazimuthalanalysisrevealedanin-planeepitaxyforbothlayers.

X-raydiffraction?-2?spectra?inthe15°–115°2?range?werecollectedforallsamplesandonlyshowedpeakscorrespondingto?00??re?ections?pseudo-cubicindexation?ofSTO,LSMO,andBFO.Figure1?d?showsthespectrafortBFO=5nmand70nm.Fromtheangularpositionofthe?003?re?ectionsofBFO,wecalculatedtheout-of-planepa-rametercBFO?4.10Åthatwasfoundtovaryonlyslightlywiththickness.Areciprocalspacemap?RSM?ofthe?103?re?ections?seeFig.1?e??fora70nm?lmshowsthatboththeLSMOandBFOlayersareveryheavilystrainedontheSTOsubstrate.NotethatnosplittingoftheBFO?103?peakisdetected,suggestingatetragonalratherthanmonoclinicorrhombohedralsymmetryfortheBFOlayer,incontrasttotheresultsofXuetal.20orQietal.,21respectively.

Figure2?a?showsamagnetizationhysteresiscycleofaBFO?5nm?/LSMObilayermeasuredat10Kwiththe?eldappliedin-planealong?100?afterzero-?eldcooling,mea-suredinasuperconductingquantuminterferencedevice?SQUID?.Thesaturationmagnetization?MS?fortBFO=5nmisabout580emucm?3,closetothemagnetizationof

bulkLSMO?590emucm?3?.22EvenforlargerBFOthick-nessvalues,thecontributionoftheBFOlayertothemagne-tizationwasnotvisible,asexpectedfromtheverysmallmagnetizationvaluesobtainedforoptimizedBFOsingle?lmsgrowninthesameconditions.19Wemeasuredtheevo-lutionofthemagnetizationwiththetemperatureinordertocheckthequalityoftheLSMOlayer?seeFig.2?b??.TheCurietemperature?TC?is330K,somehowsmallerthanthebulkTC=370K,22butingoodagreementwiththeTCofthinsingle?lms23ofsimilarthickness.

TheBFO/LSMObilayerswereimagedwithaconductive-tipatomicforcemicroscope?CTAFM?.Inthesetypeofexperiments,themorphologyofthesamplesurfaceandtheresistancebetweenthebottomelectrodeandthetiparemeasuredsimultaneously,andcoupledheight-resistancemapsarerecorded.24Examplesofsuchmaps3?3?m2areshowninFigs.3?a?and3?b?foraBFO?5nm?/LSMObi-layer.Theleftimagerevealsavery?atsurface?inagreementwiththetwo-dimensionalgrowthmodeinferredfromtheRHEEDpatterns?withterracesseparatedby?4Åhighsteps,i.e.,aperovskiteunitcell.Thecorrespondingresis-tancemap?Fig.3?b??showsahighresistancelevel?averagevalue?1G??,witharemarkablehomogeneity.SimilarcoupledmapswerecollectedforsampleswithdifferentBFOthicknesses.Identicalunit-cellstepswereobserveduptotBFO=20nm.ResistancemapscouldbecollectedforthetBFO=1,2,and5nmsamples,withoutsaturatingthecapabil-ityoftheCTAFMelectronics.TheaverageresistanceofthemapsisplottedasafunctionoftheBFOthicknessinFig.3?c?.ThedataattBFO=0correspondtoasingleLSMO?lm.AnexponentialincreaseoftheresistancewithtBFOisob-tained,whichindicatesthattransportoccursthroughtheBFO?lmbytunneling.Thisobservation,togetherwiththe?atnessandthehomogeneityoftheBFOontheLSMObuff-ers,quali?esBFOverythin?lmsaspotentialbarriersintunneljunctions.

Piezoelectricatomicforcemicroscopy?PFM?wasusedtoprobetheferroelectricityoftheBFO?lmsinBFO/LSMObilayers,25forseveralvaluesoftBFO.Analternativelyposi-tiveandnegativevoltagewasappliedbetweentheconduc-tivetipoftheAFMandthebottomelectrode?LSMO?topoletheBFOlayerinto“up”and“down”stripes.PFMwasthenusedtodetectthedomainstructure.Figure4?a?showsthetopography,andFigs.4?b?and4?c?thePFMimagesofthe5nm?lmafterwriting.WeobserveaclearcontrastinFig.4?b?thatrevealsthepresenceofupanddownferroelectricdo-mainsinthis?lm.Notethatthispatternisnotobserved

in

Downloaded 08 Apr 2013 to 219.228.57.28. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://wendang.chazidian.com/about/rights_and_permissions

额外热舞

062502-3Beaetal.Appl.Phys.Lett.88,062502?2006?

?lmsgivevirtuallynosignal,asexpectedforaweakferro-magnet.ThroughacombinedCTAFMandPFMstudyontheseBFO/LSMOheterostructures,wehaveshownthatBFOlayersasthinas5nmareferroelectricandcanbeusedastunnelbarriers.Thisopensthewayfortherealizationofseveraltypesofdevices,suchasferroelectrictunneljunctions15ormagnetictunneljunctions4withferroelectrictunnelbarriers.Inthislattertypeofstructure,acontroloftheferroelectricpolarizationbyanexternalmagnetic?eldcanbeenvisaged,viathemagnetoelectriceffect.

TheauthorsareverygratefultoM.ViretandD.ColsonforprovidingtheBFOtargetandtoJ.-M.Trisconeforfruit-fuldiscussions.Twooftheauthors?G.H.andM.S.?acknowledge?nancialsupportfromtheMinistèredel’EducationNationale,del’EnseignementSupérieuretdelaRecherche?France?.Anotherauthor?H.B.?acknowledges?nancialsupportfromtheConseilGénéraldel’Essone?France?.

S.A.Wolf,D.D.Awschalom,R.A.Buhrman,J.M.Daughton,S.vonMolnar,M.L.Roukes,A.Y.Chtchelkanova,andD.M.Treger,Science294,1488?2001?.2

A.H.MacDonald,P.Schiffer,andM.Samarth,Nat.Mater.4,195?2005?.3

J.M.D.CoeyandM.Venkatesan,J.Appl.Phys.91,8345?2002?.4

J.S.Moodera,L.R.Kinder,T.M.Wong,andR.Meservey,Phys.Rev.Lett.74,3273?1995?.5

M.Bowen,M.Bibes,A.Barthélémy,J.-P.Contour,A.Anane,Y.Lemaître,andA.Fert,Appl.Phys.Lett.82,233?2003?.6

N.A.Hill,J.Phys.Chem.B104,6694?2000?.7

M.Fiebig,J.Phys.D38,R123?2005?.8

N.A.HillandK.M.Rabe,Phys.Rev.B59,8759?1999?.9

J.Wang,J.B.Neaton,H.Zheng,V.Nagarajan,S.B.Ogale,B.Liu,D.Viehland,V.Vaithyanathan,D.G.Schlom,U.V.Waghmare,N.A.Spaldin,K.M.Rabe,M.Wuttig,andR.Ramesh,Science299,1719?2003?.10

W.Eerenstein,F.D.Morrison,J.Dho,M.G.Blamire,J.F.Scott,andN.D.Mathur,Science307,1203a?2005?.11

G.A.Smolenskii,V.M.Yudin,E.S.Sher,andY.E.Stolypin,Sov.Phys.JETP16,622?1963?.12

P.Fischer,M.Polomska,I.Sosnowska,andM.Szymanski,J.Phys.C13,1931?1980?.13

C.BinekandB.Doudin,J.Phys.:Condens.Matter17,L39?2005?.14

C.Binek,A.Hochstrat,X.Chen,P.Borisov,W.Kleemann,andB.Doudin,J.Appl.Phys.97,10C514?2005?.15

J.RodríguezContreras,H.Kohlstedt,U.Poppe,R.Waser,C.Buchal,andN.A.Pertsev,Appl.Phys.Lett.83,4595?2003?.16

H.Kohlstedt,N.A.Pertsev,J.RodríguezContreras,andR.WaserPhys.Rev.B72,125341?2005???17

M.Ye.Zhuravlev,R.F.Sabirianov,S.S.Jaswal,andE.Y.Tsymbal,Phys.Rev.Lett.94,246802?2005?.18

J.-L.Maurice,R.Lyonnet,andJ.-P.Contour,J.Magn.Magn.Mater.211,91?2000?.19

H.Béa,M.Bibes,A.Barthélémy,K.Bouzehouane,E.Jacquet,A.Khodan,J.-P.Contour,S.Fusil,F.Wyczisk,A.Forget,D.Lebeugle,D.Colson,andM.Viret,Appl.Phys.Lett.87,072508?2005?20

G.Xu,H.Hiraka,G.Shirane,J.Li,J.Wang,andD.Viehland,Appl.Phys.Lett.86,182905?2005?.21

X.Qi,M.Wei,Y.Lin,Q.Jia,D.Zhi,J.Dho,M.G.Blamire,andJ.L.MacManus-Driscoll,Appl.Phys.Lett.86,071913?2005?.22

A.Urushibara,Y.Moritomo,T.Arima,A.Asamitsu,G.Kido,andY.Tokura,Phys.Rev.B51,14103?1995?.23

J.-L.Maurice,F.Pailloux,A.Barthélémy,A.Rocher,O.Durand,R.Lyonnet,andJ.-P.Contour,Appl.Surf.Sci.188,176?2002?.24

F.Houzé,R.Meyer,O.Schneegans,andL.Boyer,Appl.Phys.Lett.69,1975?1996?.25

P.Paruch,T.Tybell,andJ.-M.Triscone,Appl.Phys.Lett.79,530?2001?.26

C.LichtensteigerandJ.-M.Triscone,Phys.Rev.Lett.94,047603?2005?

.

1

FIG.3.3?3?m2morphology?a?andresistance?b?mapsoftheBFO?5nm?/LSMObilayermeasuredsimultaneouslybyaCTAFM.?c?LogarithmoftheaverageresistanceofthesemapsfordifferentBFOthicknesses.Theerrorbarscorrespondtothefullwidthathalfmaximumoftheresistance

distribution.

thetopography.Figure4?c?,collectedafterwritingtwowiderstripesperpendicularlytothe?rstpatternofFig.4?b?,showsthatthePFMresponsecanbeswitched.ThesePFMmeasurementsarenotquantitative;sothatwecannotconcludeonapossibledecreaseofthepolarizationoftheBFO?lmwhenthicknessdecreases,asreportedforPbTiO3,forinstance.26However,theydemonstratethattheferroelec-triccharacterispreservedinBFOlayersdowntoathicknessof5nm.

Insummary,wehavesuccessfullygrownepitaxialhet-erostructuresintegratingaLSMObottomelectrodeandaBFOlayer.Thegrowthofbothlayersistwodimensional;theyareheavilystrainedandthesurfaceofthestructureisunit-cell?at.SQUIDmeasurementsindicatethattheLSMOlayerisferromagneticwithaTCof330K,whiletheBFO

FIG.4.Topography?a?andPFMimage?b?afterwritingstripedomainsusingtheAFMtipasatopelectrodeofthe5nmBFOlayer.PFMimage?c?afterwritingtwowiderstripesperpendicularlytothepatternseenin?b?.

Downloaded 08 Apr 2013 to 219.228.57.28. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://wendang.chazidian.com/about/rights_and_permissions