high-entropy alloy
073902-2Huoetal.J.Appl.Phys.117,073902(2015)
FIG.1.(a)XRDpatternsand(b)DSCtracesoftheas-castHo20Er20Co20Al20RE20(RE¼Gd,Dy,andTm)rodsindiameterof1mm.
natureofthesampleswasascertainedbyX-raydiffraction(XRD)usingaMACMo3XHFdiffractometerwithCuKaradiation.ThermalanalysiswascarriedoutinaPerkin-ElmerDSC-7differentialscanningcalorimeter(DSC)ataheatingrateof40K/min.Thetemperatureand elddepend-encesofthemagnetizationweremeasuredusingaSQUIDmagnetometer(MPMS,QuantumDesignV).
R
III.RESULTSANDDISCUSSION
TheXRDpatternsandDSCtracesoftheas-castHo20Er20Co20Al20RE20(RE¼Gd,Dy,andTm)rodswitha
diameterof1mmareshowninFig.1.Theobviousendother-micglasstransitionbehaviorsandexothermiccrystallizationpeakscanbeobservedintheDSCtraces,indicatingthefor-mationofglassyalloys.TheXRDpatternsshowbroaddif-fractionmaximaandnosharpBraggpeaksfromcrystallinephases,certifyingthefullyamorphousmicrostructureofthesamples.Theglasstransitiontemperature(Tg), rstcrystalli-zationtemperature(Tx),andsupercooledliquidregion(DTx¼Tx–Tg)arelistedinTableI.TheDTxofthesealloys,theimportantparameterinevaluatingtheirglassformingability(GFA),aresmallerthanthoseoftheotherrareearthbasedBMGsshowninTableI.ThisindicatesalimitedGFAandisconsistentwiththefactthatthecompositionsoftheseHE-BMGalloysarefarfromtheeutecticpointswherethebestGFAisusuallyfound.20
ThetemperaturedependenceofthemagnetizationfortheseHE-BMGsismeasureduponheatingundera eldof200Oe,asshowninFig.2(a).Thezero eldcooling(ZFC)branchesweremeasuredaftercoolingfrom300to2Kunderzero eld,andthe eldcooling(FC)onesweremeasuredaftercoolingfrom300to2Kunder200Oe.Aspinfreezingtransi-tioncanbeobservedintheFCcurve,whileacuspexistsintheZFCatthesametemperature.ThedivergencebetweentheFCandZFCcurvesisatypicalspin-glass-likebehavior.15Themagnetictransitiontemperatures(TC)calculatedfromthedifferentiationofFCcurvesare37K,18K,and9K,forRE¼Gd,Dy,andTm,respectively,asismarkedbyarrowsintheinsetofFig.2(a).Generally,theTCusuallytendstofol-lowthedeGennesfactor(F)intheREbasedcompounds21,22andmetallicglasses,23,24i.e.,thelargerthemagnitudeofF,thegreaterthevalueofTC.ThedeGennesfactorcanbeexpressedas:22F¼J(Jþ1)(gÀ1)2,whereJisthetotalor-bitalquantumnumber,gisthegyromagneticratioandisgivenbyg¼1þ[J(Jþ1)þS(Sþ1)ÀL(Lþ1)]/2J(Jþ1),whereSisthespinquantumnumberandListheorbitalangu-larmomentumquantumnumber.ThedeGennesfactorsofGd,Dy,andTmobtainedbytheoreticalcalculationare15.8,7.1,and1.2,respectively.AsshowninFigure2(b),theTCexhibitsagoodlinearrelationwiththedeGennesfactor.Thus,thedeGennesfactorisagoodguideforestimatingtheorderingtemperaturesinagivenlanthanidecompoundseries.
Theisothermalmagnetization(M-H)curvesaremeasuredoverawidetemperaturerangeundervariousexternal eldsupto5T.TherepresentativecurvesforHo20Er20Co20Al20Tm
20
http://www.77cn.com.cnparisonofthemainpropertiesoftheHE-BMGsdevelopedinthisworkandtherecentlyreportedrareearthbasedBMGs:theglasstransitiontemperature(Tg), rstcrystallizationtemperature(Tx),supercooledliquidregion(DTx),magnetictransitiontemperature(TC),peakvalueofthemagneticen-tropychange(jDSpkMj),fullwidthathalf-maximumoftheDSMpeak(dTFWHM),andRCundera http://www.77cn.com.cnposition
Ho20Er20Co20Al20Gd20Ho20Er20Co20Al20Dy20Ho20Er20Co20Al20Tm20Gd53Al24Co20Zr3Gd55Ni15Al30Tb55Co20Al25
Dy36Ho20Co20Al24Er50Co20Al24Y6Tm39Ho16Co20Al25
Tg(K)612632648606602614633651666
Tx(K)652668680672658680687702719
DTx(K)403632665666545153
TC(K)3718993701052384.2
À1À1
jDSpkK)Mj(Jkg
dTFWHM(K)
56
3725839947442623
RC(JkgÀ1)
627468375780606352417423429
Ref.ThisworkThisworkThiswork
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11.212.615.09.46.127.59.4915.9118.34