Structural and magnetic properties of


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J.Phys.D:Appl.Phys. (2011)395001 MnatomslocatedinthecorrespondingMnsublattice,and,to fromdiscspreviouslycutfromthecentreoftheingotsby slowspeeddiamondsaw.Thetransformationtemperatures microstructureconsiderablyvariesdependingontheCr concentration.Inparticular,theternaryalloyexhibitsasingle- phasemicrostructurewhereasasecondphasecanbeclearly distinguishedintheCr3andCr4alloysand,toalesserextent,in theCr2one.Thefractionandthemorphologyoftheappearing secondphasedrasticallyevolvewiththeincreasingamount ofCr,fromthefewgrain-boundarieslocatedprecipitates observedintheCr2micrographtothecellularanddendritic structuresshownintheCr3andCr4alloys,respectively.The chemicalcompositionofthematrixandthesecondphase appearingineachalloy,aswellastheaveragecomposition inthewholesamples,areshownintable Inallcases,thesecondphaseisricherinchromiumthan thematrixphase,pointingoutalowsolubilityofCrinthe NiMnInsystem.Uptonow,theappearanceofasecond phaseasaconsequenceofdopinginNiMnInhasjustbeen reportedfrompartialsubstitutionsofmorethan5%ofFeby In[ ]or7.5%ofCobyNi[ ],sotheobservationofa precipitatedphaseinalloyswithsuchalowCrconcentrations suggeststhatthesolubilityofCrinNiMnInisthelowest amongthestudieddopingelements.Itisworthmentioning thatnosecondphasehasbeenreportedinpreviousworkson Cr-dopedNiMnInalloys,althoughtheCrconcentrations addedtotheternarysystemsinthoseworkswerealwaysbelow 2%(at%)[ Thestructuraltransformationstakingplaceinthestudied alloyshavebeenstudiedbyDSCmeasurementsperformedon Theexothermicandendothermicpeakscorrespondingtothe forward(austenite martensite)andreverse(martensite austenite)MTscanbeclearlyobservedinthecoolingand heatingcurves,respectively,wherethetransformationpeaks showthetypicalthermalhysteresisinherenttoitsrst- ordercharacter.Asaconsequenceoftheextraenergy termassociatedwiththepresenceofthesecondphase,the transformationpeaksareconsiderablybroaderfortheCr3alloy J.Phys.D:Appl.Phys. (2011)395001 Figure1. RoomtemperatureSEMmicrographsoftheelaboratedalloys:( )Cr0,( )Cr2,( )Cr3and( )Cr4. Table1. Compositionandvalenceelectronconcentrationofthestudiedalloys. AlloyNi(at%)Mn(at%)In(at%)Cr(at%) e/a Cr050.332.517.207.821 Average50.133.115.51.37.870 Matrix50.333.315.70.77.874 Precipitates45.632.314.87.37.703 Average50.631.915.22.37.887 Matrix50.832.316.907.848 Precipitates54.931.110.33.78.198 Average49.831.115.04.17.853 Matrix49.331.3163.47.805 Precipitates51.529.511.47.68.013 and,especially,fortheCr4one[ ].TheMTtemperature andtheentropychangeattheMT( )estimatedfrom thethermogramsareshownintable hasbeentaken J.Phys.D:Appl.Phys. (2011)395001 Figure2. DSCthermogramsperformedonacooling/heating Alloy (Jkg Cr028828821136 Cr233014244 Cr330328219629 Cr428928523028 Figure3. Figure4. inNiMnInalloys[ ].Ontheonehand, shows analmostlinearincreasewiththeincreasing e/a ratio,asit doesinNiMnInalloys,albeittheslopeoftheregression lineisslightlylowerinourquaternarysystem.Ontheother, isshowntobeinsensitivetothevariationincomposition linearlydecreaseswiththeincreasing e/a ,just asitoccursinternaryalloys. Thefactthat,irrespectiveoftheCrconcentration, monotonicallyincreaseswiththematrixelectronconcentration suggeststhattheadditionofCraffectstheMTtemperatures mainlythroughthevariationinthe ratio.Inthissense, thepresenceofthesecondphaseseemsnottoaffectthe compositionaldependenceoftheremanentmatrix.Inanycase, J.Phys.D:Appl.Phys. (2011)395001 Figure5. H (1) where M DSCmeasurements(seetable )aresubstitutedinequation( theobtainedshiftsare 09KkOe forthe Cr0alloyand 05KkOe fortheCr4alloy, whichareingoodagreementwiththevaluesobtaineddirectly fromtheregressionlinesingure .Nevertheless,these Figure6. MTtemperatureshiftontheCr0andCr4alloysasa InordertoestimatetheMCE, hasbeencalculatedfrom atthehighestappliedeld.Thecalculated under60kOe J.Phys.D:Appl.Phys. (2011)395001 Figure7. 2and /T) 08for theCr0andCr4alloys,respectively(where hasbeen calculatedfromtherespectived values).Now,if /S) fortheCr0andCr4alloys, respectively,whichareinverygoodagreementwiththe resultspreventtheadditionofhighamountsofCrtoNiMnIn. Acknowledgments Thisworkhasbeencarriedoutwiththenancialsupportofthe SpanishMinisteriodeCienciayTecnolog a(Projectnumber MAT2009-07928). References [1]BrownPJ,CrangleJ,KanomataT,MatsumotoM, NeumannKU,OuladdiafBandZiebec Phys.:Condens.Matter [2]PonsJ,ChernenkoVA,SantamartaRandCesariE2000 Mater. [3]UllakkoK,HuangJH,KantnerC,OHandle yRCand KokorinVV1996 J.Phys.D:Appl.Phys. (2011)395001 IOPP OURNALOF D:A J.Phys.D:Appl.Phys. (2011)395001(7pp) stacks.iop.org/JPhysD/44/395001 1.Introduction

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