Field-Induced Ferromagnetic Order and Colossal Magnetoresistance in La_{1.2}Sr_{1.8}Mn_2O_7

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1、Field-inducedFerromagneticOrderandColossalMagnetoResistanceinLaSrMnO:a139LaNMRstudy1.21.827Y.Shiotani1,†,J.L.Sarrao2,andGuo-qingZheng1,3,∗1DepartmentofPhysicalScience,GraduateSchoolofEngineeringScience,OsakaUniversity,Osaka560-8531,Japan2CondensedMatterandThermalPhysics,MSK764,LosAlamo

2、sNationalLaboratory,LosAlamos,NM87545,USAand3DepartmentofPhysics,OkayamaUniversity,Okayama700-8530,Japan(Dated:February6,2008)AbstractInordertogaininsightsintotheoriginofcolossalmagneto-resistance(CMR)inmanganeseoxides,weperformeda139LaNMRstudyinthedouble-layeredcompoundLa1.2Sr1.8Mn2O7

3、.WefindthatabovetheCurietemperatureTC=126K,applyingamagneticfieldinducesalong-rangeferromagneticorderthatpersistsuptoT=330K.ThecriticalfieldatwhichtheinducedmagneticmomentissaturatedcoincideswiththefieldatwhichtheCMReffectreachestoamaximum.OurresultsthereforeindicatethattheCMRobservedaboveT

4、Cinthiscompoundisduetothefield-inducedferromagnetismthatproducesametallicstateviathedoubleexchangeinteraction.PACSnumbers:75.47.Gk,75.50.-y,76.60.-karXiv:cond-mat/0602161v1[cond-mat.str-el]7Feb20061Sincethediscoveryofgiantmagneto-resistance(GMR)inmagneticsuperlattices,spin-dependentcond

5、uctivityhasbecomeanimportantsubfieldofresearchinbothcondensedmatterandappliedphysics.Inrecentyears,theRuddlesden-Popperseriesofmanganeseoxides,(La,Sr)n+1MnnO3n+1,hasbeenfoundtoshowevenlargermagnetoresistance,theso-calledcolossalmagneto-resistance(CMR)[1,2,3,4].Thesecompoundshaveperovski

6、tecrystalstructurethatalsohouseshightemperaturesuperconductivity.Ithasbecomeclearthatinthesecompounds,thedegreesofspin,charge,electronicorbitalandlatticeinteractwitheachother,andareresponsiblefortherichphysicalproperties[5].Amongthem,then=2compounds,La2−2xSr1+2xMn2O7haveattractedagreat

7、dealofattention.Thecarriercontent(holecontent)canbesystematicallytunedbychangingx.Correspondingly,themagneticstructureandtheelectricalconductivitychange[2,3].Thec-axislengthisabout5-foldlargerthanthea-axis;theferromagneticMnO2doublelayersandnon-magnetic,insulating(La,Sr)2O2blockarest