DOC

Magnetocaloric

By Marvin Stevens,2014-07-23 23:30
8 views 0
Magnetocaloricto

    Magnetocaloric

Availableonlineatwww.sciencedirect.com

    ;

    ;ScienceDirect

    ;RAREMETALS,VoL25No.4tAug200&p.350

    ;RAREMETALS

    ;Magnetocaloriceffectof(Gdl-xNdx)Co2alloysinlowmagneticfield ;CHENXiang~b,

    ;ZHUANGYinghong,YANJialin,ZHOUKaiwena,andLIKefeng

    ;IKeylaboratoryofthelcfmistryofEducationofchinaforNonfeFrolg~Mca|M_aterl0|sandNewProcessingTechnology,GuangxiUniversity,Nanning530004,China ;Depo‟tmentofPhysicsandElectronicInformationalEngineering,NeijiangTeachersCollege,Neo‟iang641002,China

    ;Received5August2007;receivedinrevisedform27October2007;~cepted12November2007

    ;Ab~tract

    ;phasesandmagnetocaloriceffectinthealloys(Gdl

    Ndx)Co2withx:0,0.1,O.2,O.3,and0.4wereinvestigatedbyX-raydiffraction ;analysisandmagnetizationmeasurement.ThesamplesaresinglephasewithacubicMgCu2-typestructure.Thedecreasesobviouslywith

    ;increasing

    dcontentfrom4O4Kofthealloywithx=0to272Kofthealloywithx=0.4;forx=0.3,theis296K,whichisnearrooln

    ;temperature.Inthesamples(Gdldx)Co2withx=O.0,0.1,O.2,O.3,and0.4,themaximummagneticen~opychangeis1.471,1.228,1.280,

    ;1.381and1.610J?k?K-,respectively,intheappliedfieldrangeof0.2.0T.TheresultsofArrottplotsconfLrmedthatthetransitiontype

    ;weresecondordermagnetictrailsitionforx=0.0.3,and0.4.

    ;Keywords:magneticrefrigerationmaterials;magnetocaloriceffect;magneticentropychange;phasetransition

    ;1.Introduction

    ;Magneticrefrigerationisbecomingapromisingtechnol

    ;ogytoreplacetheconventionalgascompressmnexpansion

    ;technique.anditwillbringaboutlargesocialandeconomi

    ;calvalueonceitcomestrue.Sincethel980s.especiallyin

    ;l997.PecharskyandGschneidnerfoundthegiantmagneto.

    ;caloriceffect(GMCE)inGd5(SixGel-x)4alloys[1-3].Mate-

    ;rialswithmagnetoealoriceffect(MCE)formagneticrefrig-

    ;eratorshavebeeninvestigatedintensively.Inall,inthe

    ;rangeofroomtemperature,togaingiantmagnetocaloricef-

    ;feet(GMCE),weshouldchoosesoftmagneticmaterials, ;whichhavebigtotalazimuthalquantumnumber(,)and ;Landeg-factor,andattheSalTletime,theirCurietem

    ;peratures()arenearroomtemperature.Theoretica1ca1. ;culationshowsIrcearthelementGdanditspartintermeta1. ;1iccompoundshavebigjandgfactors,andtheyhaverela- ;rivemagnetocaloriceffect.

    ;Themaximummagneticentropychange(}ASM,)of

    ;theGdCo2alloyisabout1.5J.kg-L.K-at0.2Tlowmag

    ;neficfield,itsisabout405K[4,anditsmagneticphase

    ;transitionisofsecondorder51,whichishigherthanthatat

    ;roomtemperature(300K1.Tofurtherpromoteitsmagnetic ;propertiesandmagnetocaloriceffect,someresearchershave ;usedotherrareearthelements,suchasY,Tb,Dy,andEr,to ;Correspondingauthor.”CHENXiangE-mail:gxucx@163.cOlll

    ;substituteforGd6.91.Untilnow,thereisnoreportonthe ;useofNdtosubstituteforGd,andthus,itiswellworth ;studyingtoprovidevaluableinformationforimprovingthe ;materialpropertiesanddevelopingnewmaterials.Inthisar- ;ticle,wehavestudiedthemagnetocaloriceffectandmag

    ;neticphasetransitionintheannealedalloys(GdlNdx)Co2 ;withx=O,0.1,O.2,O.3,and0.4,whichhavenotbeenre

    ;po~edearlier.

    ;2.Experimental

    ;Five(Gdld2Co2polycrys~allinesamples,vitl1x=0, ;O.1.O.2,O.3and0.4werepreparedinanelectricarcfurnace ;underanargonatmosphereusinganon-consumabletung- ;stenelectrodeandawater-cooledcoppertray.Thestarting ;materialswereofatleast99.9%purity.Titaniumwasused ;asan0geaerduringthemeltingprocess.111ealloyswere ;re-meltedfivetimestoachievecompletefusionandhomo

    ;geneouscomposition.Toassurehomogeneity.themeltcd ;alloyswereannealedat900.Cforl0dinanevacuated ;quartztubecontainingtitaniumchipsasan0geaerplaced ;inaresistancefurnace.Thealloyswerethenfurnacecooled ;toroomtemperature.Thephasesinthesampleswereidenti

    ;fledbyXRDtl1CuKradiation(RigakuD/max2500v) ;andJADE5.0software.whichallowedrefinementofeell ;黉一

    ;

    ;Chenxet口;.Magnetocaloriceffectof(Gdl_xNdx)Co2alloysinlowmagneticfield

    ;parameters.Magnetizationmeasurementsforthesamples ;werecarriedoutusingavibrationsamplemagnetometer ;(VSM,Lakeshore7410)inanappliedfieldupto2.0T.The

    ;magnetictransitiontemperaturesinthestudiedsystemswere ;determinedwithtemperaturedependentmagnetization

    ;measurementsatanappliedfieldof0.1T.TheCurietem

    ;peratureswereidentifiedastheminimainthefirstderivative ;ofthetemperaturedependenceofthemagnetization(M-T ;curves).Themagnetocaloriceffectwasevaluatedfromthe ;calculatedmagneticentropychange6Su(T,minthevicin

    ;ityoftheCurietemperatureaccordingtothethermodynamic ;MaxwellrelationinEq.(1)[10].

    ;=r(]州?

    ;Formagnetizationmeasuredatdiscretefieldandtem

    ;peratureintervals.memagneticentropychangedefinedin ;Eq.(1)canbeapproximatedbyEq.(2)[11].

    ;M

    ;,?=[T+AT,?州一丁,,,]

    ;(2)

    ;3.Resultsanddiscussion

    ;ByanalyzingandcomparingtheX?-raydiffractionpat?- ;ternsofallsamples.asshowninFig.1.itisfoundthatall ;thesamplesaresinglephasewithcubicMgCu2?-types07080 ;20/()

    ;Fig.1.Xraydiffractionpa~ernsforthe(Gdl_xNdDCo2sam

    ;pieswith=0(1),0.1(2,0.2(3,0.3(4,and0.4(5). ;Fig.2showsthetemperaturedependenceofthemag. ;netization(M-Tcurves,measuredinanappliedfieldof0.1 ;T.andthetemperaturerangefrom170to420Kforthean. ;nealed(GdlNdx)Co2sampleswithx=0,0.1,0-2,0.3and ;0.4,respectively.Inallthestudiedalloys,thelargedropof ;M-Tcurvesco~espondstothemagneticphasetransition ;fromferromagnetictoparamagnetic.ofthesecompounds ;aredefinedasthetemperaturewhereIIismaximum. ;351

    ;andtheyarelistedinTable1.Inthisstudy,theofGdCo2 ;is404K,whichisalmostinagreementwithRefs.[4,6],and ;thevaluesoftheotherthreealloysaresensitivetothecon

    ;tentofNd,whichdecreaserapidlywiththeincreaseofNd ;content,andwhenx=0.3,theof(Gd07Nd03)Co2is296K, ;whichisnearroomtemperature.Inthepastresearch,a ;similarsituationwasobservedin(Er,Gd)Co2[8]. ;Table1.Latticeparameters,Curietemperature,andmaxi- ;mummagneticentropychangeof(Gdtdr)C02samples ;45

    ;40

    ;35

;30

    ;25

    ;20

    .I,0.2,0.3,and0.4

    ;measuredinanappfiedfieldof0.1T.

    ;Fig.3showstheisothermalmagnetizationcurves(M-H ;curves,measuredinthemagneticfieldrangeof0.2.0Tfor ;the(Gdl_xNG)Co2withx=0.1,0.2,0.3,and0.4.Calculated ;fromtheisothermalmagnetizationcurvesofFig.3usingEq. ;(2),themagneticentropychanges?-(asafunction

    ;oftemperatureonthemagneticfieldchangeof0.2.0Tfor ;thesesamplesarepresentedinFig.4.Themaximummag

    ;neticentropychangevalues(IASM.ma1)arelistedinTable1, ;andthelM.maIofthesealloysslightlyincreasewithin

    ;creasingsubstitutionofNdforGdandthemaximum ;l?M,Iis1.610J?kg?whenx=0.4.

    ;Thetypeofmagnetictransitioncanbedeterminedbythe ;Inoue.Shimizus-dmodelusinganArrottplot.Near,the ;S.shapeisfoundintheArroRplot‟scurve;itoftenindicates

    ;afirstordertransition.Ontheotherhand.iftheArrottplot ;displaysanalmostlinearrelation.itimpliesthatasec. ;?,

    ;?

    ;?

    ;t

    ;?‟

    ;??

    ;?

    ;

    ;

    ;?

    ;一一缸)r(【u.<\L10N一聂至

    ;00000O

    ;000O0

    ;505O5

    ;,,

    ;ul1()0\三至三

    ;

    ;352

    ;ond.-ordermagnetictransitionoc~ul‟s51.11leArrottplots

    ;“IVS.H/Mcurves)for=0-0.4atthe+5Kmeasured

    ;inthefieldincreasingfrom0to2.0TaleshowninFig.5. ;111eArrottplotofx=0displayslinear,whichisthecharac- ;teristicofthesecond-ordermagnetictransition,itaccords

    ;,mRe.6,91,andthesamephenomenonappearsinthe ;Arrottplotsfor=0.3and0.4.Inaddition.for=0.1and ;Magneticfieldstrength,H/T

    ;MagneticfiddstrengthHf

    ;RAREMETALS,VoL27,No.Aug2008

    ;0.2,inloweldregion,theArrottplotsshowslightly ;S.shape,andwiththeincreaseofmagneticfield‟theArrott

    ;plotsexhibitlinear.Thus,itisdi~eulttoiudgethephase ;transitionorderonlybasedO11theAn‟oRplots,andfBrther

    ;explanationfromtheLanduanmagneticphasetransition ;theoryisrequired,whichwillnotbediscussedhere. ;Magneticfieldstrength,H/T

    ;Magneticfieldstrength,H|T

    ;tag.3.Isothermalmagnetiza~oncurves(M-Tcurves)forthe(Gdl_xNdx)Co2sampleswith

    X0.I(0?2(b)‟0.3(c),and0,4(d)‟

    ;measuredatvarioustemperaturesaroundandinthemagneticfieldrangeof0-2.0T.

    ;Temperature/K

    ;Fig.4.Magneticentropychangeo一?zlc?

    ;一卑毒.v)/co一蠢矗?

    ;一卑.V\co一一苗c

    Io一蒋一苟导 ;一一卑g.《一\

    ;一卑ul\

    ;一一-I.f)/I葛一

    ;

    ;Chen.Xet口;,Magnetocaloriceffectof(Gdl-xNdx)Co2alloysinlowmagneticfield

    ;X=0.0.4werestudied.Thesecondordermagneticphase ;transitioninthesecompounds=0,0.3,and0.4)iSob. ;served.AllsamplesareofcubicMgCu2s1cnlre.andwith

    ;theNdincreasing,themaximummagneticentropychange ;lASM,ma)lslitlyincreases,whenX=0.4,l?M,ma)lis

    ;1.610J?kg(?,nolargeMCEphenomenonexistsin

    ;(GdlNdx)Co2compoundsasinGdsSi2Ge2.However, ;(GdlNdx)Co2compoundsaresensitivetoNd,rapidly ;decreaseswithincreasingNdcontent,andwhenX:0.3. ;iS296K,whichiSnearroomtemperature.Theseresultssug. ;gestthat(Gdldx)Co2hasthepotentialapplicationasa ;workingsubstanceofmagneticrefrigerationinlowmag- ;neticfield.

    ;Acknowledgement

    ;ThisstudyisfinanciallysupportedbytheNationalNatu- ;ralScienceFoundationofChina(No.50371058). ;References

    ;[1PecharskyV.K.andGschneidnerK.A…JTunablemagnetic

    ;regeneratoralloyswithagiantmagnetocalorice:ctformag

    ;neticrefrigerationfrom20to290K,App1.Phys.Lett.,1997, ;70(241:3299.

    ;[2PecharskyV.K.andGschneierK.A....JGiantmagnetocalo.

    ;ticectinGds(Si2Ge2),Phys.Rev.Lett.,1997,78:4494. ;353

    ;[3PecharskyV.K.andGschneidnerK.A.J.,Effectofalloyingon ;thegiantmagnetocaloriceffectofGds(Si2Ge2),Magn. ;Magn.Mater.,1997,167:179.

    ;[4GuZ.F.,ZhouB.,LiJ.Q.,AoW.Q.,ChengG.,andZhaoJ.C., ;Magnetocalorice:ctofGdCo2-xAlxcompounds.SolidState ;Commun.,2007,141:548.

    ;[5BuschowK.H.J.HandbookofMagneticMaterials,Elsevier, ;Amsterdam,1999.

    ;[6ZhouK.W.,ZhuangY.H.,LiJ.Q.,DengJ.Q.,andZhuQ.M., ;MagnetocaloriceffectsinGdlCo2‟SonaStateCom—

    ;mun.,2006,137:275.

    ;[7MurataK.,Ful(amichK.,FujinagaY.,SyonoY.,andGotoT., ;MagnetoelasticpropertiesofLavesphasecompounds ;(Gdl-xYx)Co2,Magn.Magn.Mater.,1995,140-144:833. ;[8LiuX.B.andAltounianZ.,Magnetocaloriceffectin ;(Erl~Gdx)Co2pseudobinarycompounds,Magn.Magn. ;Mater.,2005,292:83.

    ;[9WangD.H.,LiuH.D.,andTangS.L.,Magneticpropertiesand ;magnetocaloriceffectsin(GdxDy~-x)Co2compounds,Phys. ;Lett.A,2002,297:247.

    ;[10HashimotoT.,NumasawaT.,ShinoM.,andOkadaT.,Mag- ;neticrefrigerationinthetemperaturerangefrom10Ktoroom ;temperature:theferromagneticrefrigerants,Cryogenics,198l, ;21:647.

    ;[1lFoldeakiM.,ChahineR.,andBoseT.K.,Magneticmeas. ;urements:Apowderfultoolinmagneticrefrigeratordesign, ;App1.Phys.,l995,77:3528.

    ;

    ;

Report this document

For any questions or suggestions please email
cust-service@docsford.com