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.

497

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.

498