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1、Eur.Phys.J.SpecialTopics158,149–154(2008)THEEUROPEANcEDPSciences,Springer-Verlag2008DOI:10.1140/epjst/e2008-00668-0PHYSICALJOURNALSPECIALTOPICSMagneticandstructuralpropertiesofnon-stoichiometricNi-Mn-GaferromagneticshapememoryalloysP.L´azpita1,a,J.M.Barandiar´an1,J.Guti´errez1,M.Richard2,S.M.Allen
2、2,andR.C.O’Handley21Depto.ElectricidadyElectr´onica,Fac.CienciayTecnolog´ıa,UniversidaddelPa´ısVasco(UPV/EHU),Apdo.644,48080,Spain2DepartmentofMaterialsScienceandEng.,MIT,Cambridge,MA02139,USAAbstract.Structuralandmagnetictransitiontemperaturesofferromagneticshapememoryalloyspresentastrongdependenc
3、eonslightdeparturesfromthestoichiometry,asdoesthemobilityoftwinboundariesresponsibleforthelargemagneticfieldinducedstrains.Inthisworkwestudyfournonstoichio-metricNi-Mn-Gapolycrystallinealloyswithcompositionsof43–52at.%nickel,excessmanganeseanddeficientingallium,andasinglecrystalofcompositionNi52Mn26G
4、a22.Thosecompoundsareoftechnicalinterestduetotheobservedlargeroomtemperaturemagneticfieldinducedstrains.CalorimetricandmagneticmeasurementsdeterminedthemartensitictransitionandCurietemperaturesofthealloys(AS=331KandTCurie=366Kfor52at.%nickelalloy).Nickeldefectivealloyspresentamartensitictransitionre
5、gionbroaderthanexcessnickelones.Neutronpowderdiffractionanalysisconfirmedorthorhombicmartensiticstructuresfornickeldefectivealloys,andtetragonalforexcessnickelones.Inthe52atomic%nickelalloyscasethecrystallographicstructureofthemartensiticphasewasalsoobtainedonasinglecrystalwiththesamecomposition,trai
6、nedtogetasinglevariantinagreementwithdeterminedinthepowdersample.1IntroductionFerromagneticHeuslerNi-Mn-Gashapememoryalloys[1,2]havegreatinterestduetoanunusualmagnetomechanicalbehaviourthatopensnewpossibilitiestotechnicalapplicationsassensorsandactuators[3].Thesealloysexhibitamartensitictransitionu
7、ndergoingaustenitictomartensiticphasethroughthemartensitictransitiontemperature(TM)thatisinfluencedbyappliedexternalmagneticfieldanduniaxialstress,andalsoaferromagnetictransitionattheCurietemperature(TC)[4,5]
