High frequency magneto-impedance of double perovskite $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$ seconda

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1、Highfrequencymagneto-impedanceofdoubleperovskiteLa1.2Sr1.8Mn2O7:secondarytransitionsathightemperaturesP.V.Patanjali,P.Theule,Z.Zhai,N.Hakim,andS.SridharaPhysicsDepartment,NortheasternUniversity,360HuntingtonAvenue,Boston,MA02115R.Suryanarayanan,M.Apostu,G.Dhalenne,andA.Revcolevschi,Lab

2、oratoiredeChimiedesSolides,UA446,UniversitˇeParis-Sud,91405Orsay,FranceRadiofrequencymagneto-impedancemeasurementsrevealapronouncedanomalyat260Kbe-sidesthemainMItransitionat125KinthedoubleperovskitematerialLa1.2Sr1.8Mn2O7.Thisfeatureisnotseenclearlyinstaticresistivityandmagnetizationme

3、asurements.Wesuggestthatthisanomalyrepresentsshort-rangemagneticcorrelationsenhancedatradiofrequencies,withtheeasyaxisalongthec−axis.Theobservationofcolossalmagnetoresistance(CMR)tiononthecollectiveresponseofspinandchargedynam-inperovskitemanganitesLa1−xAxMnO3(A=Sr,Ca)ics.Inthisreportw

4、edescribe,forthefirsttime,temper-[113]hastriggeredfurtherresearchintorelatedsystemsatureandfielddependenceofradiofrequencydynamic[1–4].TheCMRinthesematerialsisnormallyob-responseofthedoubleperovskiteLa1.2Sr1.8Mn2O7.Weservedattemperaturesclosetotheferromagnetic-to-focusonapronouncedanomal

5、yaround260Kobservedparamagnetictransitionassociatedwithametalinsu-inmanysamplesandsuggestthatthisanomalyrepre-lator(MI)transition.Followingthedoubleexchangesentsmagneticcorrelations,perhaps2-Dinnature,withmechanismofZener[5],baseduponthestrongon-siteasingleenergyandtemperaturescale.(Hu

6、nd’srule)couplingbetweenthechargecarriers(eg-Singlecrystals(5cmlongand0.5cmdiameter)oflikestate)andthelocalspins(t2g-likestate),severalLa1.2Sr1.8Mn2O7weregrownfromthemeltbythemodels[6–10]havebeenproposedtoaccountforthesefloating-zonemethodusingamirrorfurnace[19].Powderproperties,butmany

7、oftheobservedfeaturescannotX-raydiffraction(XRD)analysisresultedinthelatticebeaccountedbythedoubleexchangeinteractionalone.parametersa=3.864±0.002˚Aandc=20.130±0.006˚AThesewell-studied113compoundscanbeconsideredas,incloseagreementwiththosepreviouslyreported[15].then=∞membersoftheRuddl