Magnetization of CeAg at high pressure

Volume84A, number9 PHYSICSLETTERS 31 August1981

MAGNETIZATION OF CeAgAT HIGH PRESSURE

Makio KURISU, Hideoki KADOMATSU andHiroshi FUJ1WARADepartmentofMaterials Science,Facultyof Science,HiroshimaUniversity,Hiroshima 730,Japan

Received21 May 1981

Magnetizationmeasurementsfor CeAgunderhydrostaticpressuresup to 4.0 kbar andCeAg1_~ln~compounds(0.01

‘~ x ~ 0.20)at normalpressureweremadeat4.2 K in magneticfields up to 50 kOe. It wasfound thatthe magnetizationof CeAgunderpressureandof CeAg .~ mx werelarger thanthatof CeAgat normalpressure.

The intermetalliccompoundCeAgshowsa struc- pliedmagneticfields up to 50 kOegeneratedwithatural distortion from cubicto tetragonalat TM = 16 K superconductingmagnet.Thepressureswere generatedasthe temperatureis lowered,andbecomesferromag- in a miniaturepiston—cylinderclamppress~1recell ofneticbelow theCurie temperatureTc = 5.5 K [1]. Be—Cu,wherethepressuretransmittingmediumwasaTherefore,it is to be expectedthat themagneticchar- mixtureof 1 : 1 n-pentaneandisoamylalcohol,andacterof CeAgis not independentof the distortiondue thehydrostaticpressurecouldberetainedby coolingto the closenessof TM andTc.The purposeof our in- thecell andsampleslowly down to the liquid heliumvestigationis to elucidatethe above-mentionedsitua- temperaturerange.Thepressurenear4.2K was deter-tion from both thepressureeffectandthealloying ef- minedfrom the pressuredependenceof thesupercon-fect by substitutingIn for Ag, sincewe believethat the ducting transitiontemperatureof Snby measuringthepressureandalloyingeffectsarecomplementaryto each acsusceptibilitywith a Hartshornbridgecircuit. It wasother. foundthat the pressuresat 4.2 K were reducedby 2.4

In a previouspaper[1], we reportedthepressureef- kbar from thoseat room temperature.In order to re-fect on TC andTM determinedfrom anelectricalresis- ducethe magnetizationof the pressurecell itself,tivity measurementfrom 4.2 K to 300 K underhydro- dummyBe—Cu cells wereconnectedto bothendsofstaticpressuresup to 5 kbar, andbothTC and TM in- thepressurecell andothercontrivanceswith respectcreasedwith increasingpressure.Quiterecently,Eiling to thesmoothsettingof thewhole cell assemblywereandSchilling [2] haveextendedtheresistivitymeasure- made.Detailsof the pressureanddummycellswill bementup to 40 kbar andfounda maximumat a pres- describedin a separatepaper[3] togetherwith ade-surep 7 kbarin the pressuredependenceof Tc. The scriptionof the magnetometer.presentpapergives theresultsof themagnetization Fig. 1 showsmagnetizationcurvesof CeAgatvar-measurementof CeAgat 4.2 K underpressuresup to 4 iouspressuresasa functionof the effectivemagnetickbarand that of CeAg1_~In~withx in therangebe- field Heff; the closedandopencirclesindicatetheex-tween0.01 and0.20at normalpressure. perimentalpoints in the initial magnetizationprocess

Polycrystalsof CeAg and CeAg1 ~In~ (x = 0.01, andwith decreasingmagneticfield, respectively.The0.02,0.03,0.05, 0.10and0.20)were preparedin ac- magnetizationsubsequenttothedemagnetizationwascordancewith theprescriptionof ref. [1] and the found to bereversible.It is notedthat thesamemag-sampleswereof sphericalform, 3—5 mm in diameter. netizationcurvesasshown in fig. 1 wereobtainedaf-Magnetizationcurveswere measuredby a vibrating ter thesamplewaswarmedup to roomtemperaturesamplemagnetometerwith a frequencyof 2 Hz in ap- andcooleddown againto 4.2K. Theresultsare ar-

rangedasfollows.

496 0 031—9163/81/0000—0000/s02.50© North-HollandPublishingCompany

Volume84A,number9 PHYSICSLETTERS 31 August1981

o-(~/f.u.) which would be lockedalongthetetragonalaxis,oc-

0:~h1 .G curstowardsthefield directionand themagneticfieldintensitywasnot strongenoughto completethedo-= •Okbaj 1.0 main rearrangementat highpressures.Therefore,theexperimentalfact thataat 4 kbarislowerthanthatatnormalpressuredoesnotseemto beserious.3.1Ic bar As a complementaryresult tothe pressureeffect,1.0 the magnetizationcurvesof theCeAg1_~In~system— P~2.1kb~r for variousIn concentrationsaregiven in fig. 2. It0~

1.0 similar to thoseat highpressures.In this alloying ef-

0 _~7~P=1.bar~ shouldbe notedthat themagnetizationprocessesarefect, the rapidincreaseandits shift tohighermagnetic0 fieldsin the initial magnetizationcurvesarewell de-

1.0 fined. Theyprobablyoriginatefrom anincreasein the

inducedmagnetocrystallineanisotropywith pressure0 or In concentration.a ~ P1k bar The magneticpropertiesof CeAgat normalpressure

________3.50 CeAg and temperatureslower than TM havebeenconsidered

0 I so far [4,5] by takinginto accounttheeffect of the

structuraldistortionat TM from cubicto tetragonalonat 4.2KC——— 0

_________ the electronicstructure;that is, this distortionsplits0 10 20 30 40 50

H~f(kOe)

Fig. 1. Magnetizationcurvesof CeAgatvariouspressures a-( JiB /f.u.)andatemperatureof 4.2 K.

1.0

At normalpressurep = 0 kbar,the magnetization

0.5 xro.1o11

XO.20’

a,in unitsof the Bohr magnetonper formulaunit,p~/fu,increaseswith increasingHeff, indicatingaratherlargehigh field susceptibility,and themagni-tudeat 50 kOeis 0.94I.LB/fu. Thespontaneousmagnet- x~o.oizationobtainedby extrapolatingsmoothlybackto 0 — I

zerofield in the decreasingcurveis about0.7pBIfu. 0

Thisvaluealmostagreeswith0.7 ±0.15,1B/fu ob- —

tainedfrom a neutrondiffraction measurementat 4.2 0 —

0K [4]. At 1.2 kbar,themagnetizationat 50 kOeis1.0

1.15~B/fu, which is considerablylargerthanthatatnormalpressure;that is, themagnetizationincreases 0

0with increasingpressure._________ 0.5However,a commentwill bemadeon theinitial ________

magnetizationprocess.Theinitial magnetizationcurve 0 — CeA~..XInX0 I

at 1.2 kbartendsto increaserapidly around5 kOe; this at 4.2rapid changeof increaseislikely to shift to higher _________ 0

magneticfields andto becomevague,aspressurein- C0—1~——20—3040 50

creases,andthemagnetizationstopsincreasingwith H~ff(kOe)pressure.Theseresultsarepossiblydue to thecircum- Fig. 2. Magnetizationcurvesof CeAg1_~In~compoundsatstancesthat the rearrangementof magneticdomains, normal pressureanda temperatureof 4.2 K.

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Volume 84A,number 9 PHYSICS LETTERS 31 August1981

thegroundstater8 quartetinto two doublets(4f in- with pressureor alloyingmay alsobeattributedto thisducedJahn—Tellereffect [6]). Both experimentalfacts increaseof occupationin the above-mentionedsense.at normalpressure,thata sharpincreasein the temper- In this case,however,theexchange-splittedlevelswouldaturecoefficientof the resistivity wasfoundbelow TM be widenedby enhancement.of the s—f interactionre-[1,7], andthat the spontaneousmagnetizationat 4.2K sulting from thed bandsplittingwith pressureor alloy-in thepresentwork is 0.7~B’ mayalsobe understood ing (bandJahn—Tellereffect [8]).in this scheme,sincetheexpectedmagnetizationfrom A carefulexaminationof thediscriminationbe-r8 is about

2/.LB. tweenthe proposedtwo kinds of Jahn—TellereffectsForthepurposeof understandingthe resultsin the [6,81 shouldbethenextproblemto beconsidered.

presentwork, however,we mayproposetheadditionalassumptionsthat(i) thehigherandlower statesof the Referencesabove-mentionedtwo doubletsarethosecarrying highandlow magneticmoments,respectively,andthe split- [1] H. Kadomatsu, M. Kurisu andH. Fujiwara,Phys.Lett.

ting betweenthetwo doubletsis relativelysmall since 70A (1979)472.- . . .. [2] A. Eiling andJ.S.Schilling,Phys.Rev. Lett. 46 (1981)

thetetragonaldistortionis small(~2%)[4], and (n) 364.eachdoubletundergoesanexchangesplittingbelowTC. [3] H. Kadomatsuet al., to bepublished.Then,theseexchange-splittedlevelswill be widened [4] D. Schmitt, P. Morin and J. Pierre, J. Magn.Magn.Mater.

withappliedmagneticfield H. As a result,the levels 8 (1978)249.

with highandlow momentsof the respectivestates [5] H. Ihrig and S. Methfessel,Z. Phys.B24 (1976)385.- . . . [6] D.K. Ray and1. Sivardiere Solid StateCommun. 19would be mixed, sothatthe occupationrn the high- (1976) 1053.

momentlevelincreasesor themagnetizationmcreases, [7] H. Ihrig andW. Lohmann, 1. Phys. F7 (1977)1957.

with increasingH. The increaseof themagnetization [8] H. Ihrig andS. Methfessel,Z. Phys.B24 (1976) 381.

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