Co掺杂对Ni—Mn—Sn铁磁形状记忆合金磁性质的影响-论文.pdf

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Availableonlineat、^n^n^，．sciencedirect．com一Transacfionsof繇ScienceDirectNonferrousMetals爱SocietyofChinaPressTrans．NonferrousMet．Soc．China24(201411053—1057www．tnmsc．cnEffectofCosubstitutiononmagneticpropertiesofNi·——Mn。——SnmagneticshapememoryalloysJia—muCAO，Chang—longTAN，Xiao—huaTIAN，Qin．ciLI，Er-junGUO，Li．pingWANG，Yi-jiangCAO1．SchoolofAppliedScience，HarbinUniversityofScienceandTechnology,Harbin150080，China；2．SchoolofMaterialsScienceandEngineering，HarbinUniversityofScienceandTechnology,Harbin150080，ChinaReceived27March2013；accepted15October2013Abstract：TheefrectofCosubstitutiononmagneticpropertiesofNi-Mn—Snshapememowalloywasrevealedbyfirst．principlescalculations．LargemagnetizationdiferenceinNi-Mn—SnalloyobtainedbyadditionofCoarisesfromenhancementofmagnetizationofausteniteduetochangeofMn-Mninteractionfromanti．ferromagnetismtoferromagnetism．TbtalenergydiferencebetweenparamagneticandferromagneticansteniteplaysanimportantroleinmagnetictransitionofNi-Co-Mn-Sn．ThealteredMn3dstatesduetoCosubstitutiongiverisetodiferenceinmagneticproperties．Keywords：feromagneticshapememo~alloys；Ni——Mn-Sn；first—principlescalculation；magneticpropertiessubstitutionofCoforNiinNi一Ⅳ【n—Snalloysisan1IntrOductiOnefectivewaytoincreasethediferenceinmagnetizationbetweenausteniteandmartensitephases『15，161．0fr．stoichiome仃icNi-Mn-SnferromagneticshapeRecently,themagneticpropertiesofNi—Mn—SnandmemoryalloyshaveattractedgreatinterestduetotheNi—Co—Mn—Snalloyshavebeenstudiedbyneutronobservationsofmagneticfield．inducedreversepowderdiffractionsanditisfoundthattheferromagneticmartensitic仃ansformation『1—41．ThemagnetizationinenhancementinNi—Co-Mn-Snocc~sasresultofthemartensitephaseofthesealloysissmallerthanthatinchangeinthemagneticstructureduetothesubstitutiontheausteniteone．Ni—Mn—SnalloysundergomartensiticofCo『16]．Sofar,althoughCosubstitutionhastransformationinamagneticallyorderedstate，andtheprominentefectsonmagneticpropertiesandmagneticinterplaybetweenthestructureandmagnetismgivesrisefield．inducedreversemartensitictransformation．thetogreatinterestingeffectssuchasinversemechanismforthemisstillunclear．magnetocaloricefect[5—8]，giantstrainduetoInthiswork．werevealedtheeffectofCofield—inducedreversemartensitic仃ansformation『9，101，substitutiononmagneticpropertiesofNi2CoxMnl+ySnlandgiantmagnetoresistivity[1l，12]．ThesemakefromtheelectronicstructurepointofviewbyNi—Mn—Snalloysgoodcandidatesformultifunctionalfirst．principlescalculations．Theresultsprovidetheapplication．Alargemagnetizationdiferencebetweentheoreticaldataanddirectionsfordevelopinghigh．theausteniteandmartensitephasesisofgreatperformancemetamagneticshapememoryalloyinimportancetodevelophigherperformancebothinNi-Mn—basedHeusleralloyssystem．magnetoelasticpropertiesandinmagnetoca1oricefect，duetotheimprovedpossibilityofdrivingstructural2CalculatiOnalmethods仃ansformationbymagneticfields．ThemagneticpropertiesoftheausteniteandmartensitephasesintheFirst-principlescalculationshavebeenperformedNi—Mn—Snalloyshavebeenintensivelystudiedbymanybasedonthedensityfunctionaltheory,usingCASTEPresearchers『13一l81．Ithasbeenreportedthatthecode[19]．TheinteractionbetweenionsandelectronsisFoundationitem：Project(1253-NCET-009)supportedbyProgramforNewCenturyExcellentTalentsinHeilongjiangProvincialUniversity,China；Project(1251G022)supportedbyProgramforYouthAcademicBackboneinHeilongjiangProvincialUniversity,China；Projects(50901026，51301054)supportedbytheNationalNaturalScienceFoundationofChinaCorrespondingauthor：Chug—longTAN；Tel：+86—451—86390728；E—mail：changlongtan@hrbust．edu．cnDOI：10．1016／S1003-6326(14)63161-7 1054Jia-muCAO，etal／Trans．NonferrousMet．Soc．China24(2014)1053—1057describedbyultra．softpseudopotentials『20]．Thespin-polarizedgeneralizedgradientapproximationwas一14391．25usedtodescribetheexchangecorrelationenergy．Theplane—wavecutofenergywas400eVanda(8，8，8)Monkhorst—Packgridwasemployedtosamplethe一l4391．50Brillouinzone．ForthecubicL2structuresofNi2Mnl-ySnl-y0J，=0，0-25，0．5)，16·atomuniteelljsbuilt—14391．75withappropriateSnatomsreplacedbyMnatoms．InthecaseofCosubstitutionforNi，thecubicstructureofNi2CoxMnl+ySnl—y=0，0．25，0．5；=0，0-25，0．5)is—14392．0ObuiltwithappropriateNiatomsreplacedbyCoatomsonthebasisofNi2Mn】+，Sn卜、structure．5．96．O6．16-23ResultsanddiscussionLatticeconstant／盖一14079．8ForthecubicphaseofNi2MnSn，themagneticinteractionbetweenMnatomsisferromagnetic．However,inthecaseofNi2Mnl+vSn1．vandthe—14080．0【1．；0)corespondingalloyswithCosubstitutionforNi，the【l_n_J．>0)一l__J．Q一originofmagneticinteractionisstillopen．Thus．weflrst—14080．2calculatedtheequationofstatesofNi2xCoxMnl+ySnl—vcubicphases，takingintoaccounttwosituationsthatmagneticmomentofexcessMnattheSnsites(denoted—14080．4asMnsn)isparalleloranti—paralleltothatofMnattheMnsites(denotedasMnMn)．Forbothsituations．itisnotedthat．ifstartingwithparalleloranti—paralle114080．65．96．06．16．2Mn—Mnmagneticcoupling，thespin-polarizedLatticeconstantself-consistentcalculationsconvergetothesolutions—13768．0withoutchangingtheinitialmagneticorientation．Hereafter,theparallelandanti．paralle1Mn-Mnmagnetic—13768．2interactionsaredenotedasPandAPstates，respectively．Figure1showsthecurvesoftotalenergyEversus—13768．4latticeconstantsforNi2CoxMnl+vSn1一v(0，0_25，0．5；0．25)cubicphases．FromFig．1(a)，itisseenthataroundequilibriumlatticeconstant，theAPstateof—13768．6Ni2Mnl~ySnl—v(0．25)ismorestablethanitsPstate．Thelatterbecomesmorestableonlyifthelatice—13768．8constantisexpanded．ThisindicatesthatthemagneticmomentoftheMnsninNi2Mnl+Snl一cubicphaseis—13769．05．96．06．16．2anti—feromagneticallycoupledtothemagneticmomentLatticecOnstant／AofMnMn．Thus，itisexpectedthatwithexcessMnsubstitutionforSn，thetotalmagneticmomentdecreases，Fig．1EquationofstatesofNi2CoxMnl+ySnl-y0，0．25，0．5；whichisagreementwiththeexperiments[18]．However,y=0．25)cubicphasesforbothparallelandanti—parallelinthesimilarNi—Mn-Inmetamagneticshapememorymagneticinteractions：(a)=0；(b)0．25；(c)0．5alloy,themagneticmomentperformulaincreaseswithincreasingMncontent．OurpreviousstudiesshowthatstablethantheAPstateatequilibrium1atticeconstant．misoppositeconcentrationdependenceisattributedtowhereasthelaterismorestablewhenthesystemisthediferentcouplingconditionsofmagneticmomentcontracted，asshowninFig．1(b)．However,theenergy『211．InthecaseofNi-Mn-Inalloys，theMn-Mndiferencebetweentwostatesismuchsmal1．Figurel(c)interactionbetweentheMnatomsatMnandInsitesisshowsthatwiththefurthersubstitutionofCoforNisuggestedtoprefertheferomagneticcoupling．In=0．5)，thePstateofNi2xCoxMnl+ySnl-y【0．5，=0．25)contrasttothecaseofNi2Mna+ySnl-yCv=0．25)．whenobviouslybecomesmorestablethantheAPstateatsubstitutionofCoforNiwithx=0．25，thePstateofequilibriumlatticeconstant．Moreover,forNi2一CoMnl+ySnl-y=0．25，Y=0．25)isslightlymoreNi2-xCoxMnl+ySnl-ywith0．5，theefectofCo —I一．J．∞j—IIog0—III1Jia—muCAO，etal／Trans．NonferrousMet．Soc．China24(2014)1053—10578761055543substitutionforNionmagneticinteractionsissimilartoferromagneticactivator,Suchahighmagnetizationthatwithy=0．25．Therefore．itissuggestedthatfordifferenceprovidesastrongdrivingforceformagneticNi2CoxMnl+vSnl—vwithx>0．25，thePstatewouldbefield—inducedtransformation，makingthismaterialamorestablethanAPstate．ThissuggeststhatMn-Mnpromisingcandidateformagneticactuationapplications．magneticinteractioninthecubicphasesofNi—Mn—SnActually,theferromagneticactivationeffectofCohashasbeenturnedfromanti—ferromagnetismtoalsobeenverifiedbyourtheoreticalcalculationinotherferromagnetismbysubstitutionCoforNi．HeusleralloyssystemsuchasNi-Mn-SbandMn—richTheconcen仃ationdependencesofthemagneticNi—Mn—Ga．Thus．thesubstitutionofCoforNiisamomentperformulaunitforNi2Mnl+ySnlyandgenera1waytoenhancethemagneticfield．inducedNi2CoxMn>ySn>y0．25)cubicphasesareshownin仃ansformationinNi—Mn-XrX=Ga，SnandSb)alloys，Fig．2．ItcanbeseenthatthemagneticmomentwhichisveryusefulfortheapplicationandmaterialdecreaseswithincreasingMncontentf1inthedesignofmetamagneticshapememoryalloy．Ni2Mnl+ySnwyalloys．whileincreasesintheFromtheapplicationpointofview,theCurieNi2-xCoxMnl+ySnl-y0．25)．Thissuggeststhatthetemperature()isveryimportantsinceitlimitsthemagnetizationofthehightemperaturecubicphaseinoperationaltemperaturerangeofNi—Mn—Sn．basedNi2Mnl+ySnl—visenhancedbythesubstitutionofCoforalloys．InordertoinvestigatetheefrectofCoNi．Furthermore．wehaveperformedthegeometrizationsubstitutionforNionTc，thetotalenergiesofbothforNi2-xCoxMnl+ySn~-y，andfoundthatthecubicphaseisferomagneticandparamagneticcubicphasesofenergeticallyfavorableforNi2MnSn．Interestingly,theNi2Mnl+ySnl-yandNi2-xCoxMnl+ySnl-y0．25)alloyscubicphaseisunstableagainstthetetragona1distortionwerecalculated．Itisfoundthatthetota1energyofforNi2-xCoxMnl+ySnl-y(0．25，0．5)andundergoestheparamagneticcubicphaseismuchhigherthanthatofthemartensitictransformationtoformtetragona1martensite．feromagneticoneatallthecompositionsstudied，whichItshouldbenotedthatbothinthemartensiteofisconsistentwiththefactthattheparamagneticcubicNi2Mnl+ySnl-yandNi2—CoxMnlSnl—y，themagneticphaseisthehigh-temperaturephase．AccordingtothemomentofMnsisalwaysanti-paralleltothatofMnMn．Stonertheory,thetotalenergydifferencebetweentheTheanti—parallelarrangementoftheMnsn-MnMnparamagneticandtheferomagneticstate，，cangivemagneticmomentcausesthedecreaseoftotalanestimationof．Thelinkbetween△andisgivenmagnetizationofmartensite．by△E=一己whererepresentstheratioofMtoM0ofthemagneticmomentMatTO0KandtheequilibriummagneticmomentM0at0K『221．Ourstudiesshowthatthetotalenergydifferenceincreasesbyabout140meVwhenNiissubstitutedby6．25％Co(molefraction；／_x=O．25)forNi2CoxMnl+ySn>ycomparedwithNi2MnlySnl—y．EventheStonertheorycannotbeappliedtodescribinghigh—temperaturemagneticproperties，ofNi2CMn1+vSn1-valloysincreaseswiththeCocontent，whichisinfairagreementwiththeexperimentalobservations『151．ThereasonforincreaseofshouldbeattributedtotheenhancedferomagneticexchangeduetoCosubstitutionforNi．00-2O．40．60．81．0TogainfurtherinsightintotheoriginofefectofCoVsubstitutiononmagneticpropertiesintheNi-Mn—Sn．Fig．2ConcentrationdependenceofmagneticmomentpertheelectronicstructureofNi2Mnl+ySnl-y(0．25)andformulaunitforNi2MnlSn】andNi2CoxMn>ySn~Ni2~CoxMnl+ySnl-y(0．25，，=0．25)wasstudiedasanf0．25)example．Figure3fa1illustratesthedensityofstates(DOS)forthecubicphaseofNi2Mnl+ySnl-y(0．25)．ItcanbeseenfromFigs．1and2thatthelargeMn3dstatesofmajorityandminorityspinaresplitwithmagnetizationdiferenceinNi-Mn——SnobtainedbyrespecttotheFermileve1．ThisdistributionmakesMnadditionofCoarisesfromsubstantialenhancementofmostlyresponsibleforthemagnetization．Moreover,itthemagnetizationofthehigh—temperaturecubicphase．canbenotedthatthemagneticmomentofMnsnisThiscanbeattributedtoachangeofmagneticstructureanti-paralleltothatofMnMn．Ni3dstateshavesimilarcausedbythesubstitutionofCoforNi，whichturnsthedistributioninthemajorityandminorityspin，resultingMn——Mninteractionfromanti-ferromagnetismtoinarathersmallmagnetization．Figure3fb1showstheferromagnetism．Therefore，theCoatomsworkasaDOSforcubicphaseofNi2xCoxMnl~ySnwy(=0．25， 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