MAGNETOCALORIC EFFECTS IN INTERMETALLIC COMPOUNDS-.ppt
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MAGNETOCALORIC EFFECTS IN INTERMETALLIC COMPOUNDS-.ppt

MAGNETOCALORICEFFECTSININTERMETALLICCOMPOUNDS-TOGUS.ppt

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MagnetocaloriceffectsinintermetalliccompoundsTcTNMagneticfield-inducedtransitionSuperconductingmagnetPermanentmagneticfieldMagneticrefrigerantmaterialsAdiabatictemperaturechangeOrderingT:TC=295KFieldchange:ΔB=5TFWHM:δTFWHM=65KMAXentropychange:-ΔSm(max)=8.5J/kgKRelativecoolingpowerRCP(S)=-ΔSm(max)*δTFWHM=552J/kgCoolingpowerExperimentalresults&discussionTC=298KΔB=2TΔTad=1.7KFirst-ordermagneticphasetransition&MCEWhatmakesGd5Ge4-xSixhavegiantMCE?B-TphasediagramMagnetizationMagneticentropychangesSpecificheatcapacityΔTad=Tc•ΔSm/Cp>15KTransitionatTC=240.0±1.0KT’C=236.0±1.0KThermalhysteresisΔT=4KΔLa/La=6.8x10-3>0ΔLb/Lb=-2.0x10-3<0ΔLc/Lc=-2.1x10-3<0RelativevolumechangeΔV/V=2.7x10-3Clausius-ClapeyronrelationdTC/dp=3.2±0.2K/kbarTransition-metalbasedcompound:MnFeP1-xAsxCompositiondependenceofTC160-330KB–TphasediagramofMnFeP0.45As0.55MagneticentropychangesIsothermalmagneticentropychanges:ConclusionsMCEiscloselyrelatedtothecriticalbehaviorofmagneticphasetransition.SecondordertransitiongivesbroadMCEpeak.MCEissmall.FirstordertransitiongivessharpMCEpeak.MCEcanbelarge.2.Gd5Si1.7Ge2.3hasasimultaneousstructuralandmagneticphasetransitionat239K.Thistransitionisafirstordertransitionwiththermalhysteresis7.4Kandwithfieldhysteresis1T.TheMCErelatedwithfirstorderphasetransitionisquitelarge.EffectofmagneticanisotropyonMCEinthismaterialisnegligible.MnFeP1-xAsx(0.25<x<0.65)hasafirstorderphasetransitionwiththermalhysteresis3.4Kandfieldhysteresis0.5T.TheMCErelatedwiththistransitionisalsoquitelarge.4.AdvantagesofMnFeP1-xAsxasamagneticrefrigerant1.LargeMCE2.Tunableorderingtemperature(between168and332K)3.Smallhysteresis4.Lowercost:MnFe(P,As):Mn,Fe,P,As(99%,150$/kg)Gd-Si-GeGd:Gd(4N):4000$/kg.Fe-Rh:Rh:12000$/kgAcknowledgmentThisworkissupervisedbyE.Brück,J.H.K.Buschow,F.R.deBoer.Collaborators:L.Zhang,W.Dagula,X.W.LiFinanciallysupportedbytheSTW.Bean-RodbellmodelGibbsfreeenergyG=Gex+GH+Gdist+Gentr+