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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