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Submitted on 1 Jan 1978
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MAGNETIC ORDERING IN CeB6 SINGLE
CRYSTALS
K. Winzer, W. Felsch
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, supplément au n° 8, Tome 39, août 1978, page C6-832
MAGNETIC ORDERING IN CeB, SINGLE CRYSTALS 6
K. Winzer and W. Felsch
I . Physikaliaohes Institut der VniversitSt GSttingen and SFB 12.6, Z400 GSttingen, Bunsenstr.9, West Germany
Résumé.- La variation thermique de la résistivité des monocristaux de CeBç montre une anomalie à 2,5 K. qui est du type de celle de Fisher et Langer. En outre il apparaît une forte anisotropie de l'aimantation et de la susceptibilité, et les courbes d'aimantation mettent en évidence une transition métamagnétique.
Abstract.- Resistivity measurements in CeB6 show-a pronounced anomaly of the Fisher-Langer type at 2.5 K Magnetic susceptibility and magnetization reveal a strong magnetic anisotropy and a metamagnetic phase transition.
INTRODUCTION.- CeB5is interesting because
it shows a magnetic phase transition below 3 K. From measurements of the resistivity and magnetic suscep-tibility it was inferred that it orders antiferroma-gnetically 111, but details of the actual spin arran-gement are unknown. Susceptibility measurements at elevated temperatures indicate that Ce is trivalent in CeB6 with a crystal field splitting of the 2Fs/2 free-ion multiplet into a Vy ground doublet and Ts
quartet separated by about 300 K 111. In solid solu-tions with isostructural (CsCl - type) LaBe, CeB6 leads to pronounced Kondo anomalies /3/. Here, for the first time, we report on measurements of the re-sistivity and magnetic susceptibility on CeB6 single
crystals.
EXPERIMENTAL.- CeB6 single crystals have been grown by an arc floating zone technique M / from 4N pure Ce and B. The crystals were analyzed by x-ray diffraction. A parasitic phase could not be detected. Samples of about 10 mm length and 1.8 mm diameter were used. Low frequency a.c. resistivity and suscep-tibility measurements in magnetic fields up to 50 kOe were performed in an adiabatic demagnetization cryos-tat down to 50 mK. The magnetization was obtained from the susceptibility by integration.
RESISTIVITY.- figure 1 shows the resistivity of CeBjand LaBe single crystals as a function of temperature for j || 110 (other current directions show nearly the same results). The resistivity of LaB6 (RRR = 50) was subtracted to obtain the magnetic
contribution p (T) of the resistivity of CeBe. This magnetic contribution shows a strong increase between
IK and 2.5 K, a point of inflection at T = 2.38 K c
(see insert in figure 1) followed by a weaker in-crease with a maximum at 3.5 K and a strong decrea-se to higher temperatures. The inflection point of pm (peak in the derivative dp /dT) occurs at almost
m
the same temperature as the peak in the zero-field susceptibilities (figure 2 ) . 8 0 - j s o - /r \ 8LOB6 g 50- v f \
G \
4- / J \
*• ^2-
J \ I \.
30- •«. \ ! S ^ ^ ^ 2 0 - 236 2X 2*0/ ^*""""«*7 ^^
o I i •• c i—i 1—f • t ~ " T i — H 0.1 02 OS t 2 5 10 20 50 100 200F i g . l R e s i s t i v i t y of CeBg and LaB$ s i n g l e c r y s t a l s versus temperature.
I n s e r t : temperature dependence of dp /dT
near T . m
c
Such a type of behavior of the magnetic re-sistivity was predicted by Fisher and Langer /5/ who argued that the resistivity anomaly at the cri-tical point of a metallic ferro- or antiferromagnet is dominated by electron scattering from short ran-ge spin fluctuations. The result of their calcula-tion is a resistivity anomaly with a rounded maximum above T and a singularity in the
Fig. 2 Temperature dependence of the initial suscep- tibility of CeBs single crystals.
In a preliminary attempt to estimate the critical parameter describing the anomaly in dp /dT
m the results were fitted to the usual expression for critical phenomena
with E= (T-Tc)/Tc and A,B constants. For T >Tc ( l d 3 < E . < 2 x lo-') the best fits were obtained with Tc = 2.375 K, 1 = 1.1
+
0.1. The positive lo- garithmic divergence of dpm/dT both above and below Tc indicates that the magnetic reciprocal lattice vector K in CeB6 is smaller than the inverse of them
cbrrelation length of the spin fluctuations 161. A small value of K would agree with a helical or
m
screw spin ordering as in other rare earth metals and compounds. Cornut and Coqblin 171 have shown that in similar compounds, like CeA12, both the Kondo effect and crystal field effects give a contribution to the resistivity. While it cannot be excluded that the steep decrease of pm for T >> T may be partly to the Kondo effect, no indication of a crystal field contribution (a maximum of p at a temperature around
m
the crystal splitting A
-
300 K / 7 / ) is found in the data.below 4 K. This anisotropy is alos apparent in the magnetization curves as demonstrated in figure 3, where the magnetization M per Ce ion at T = 70 mK is plotted versus the external field applied. We note that 110 is the easy axis of the magnetiza-
1 1
tion, the curves show inflection points and the100 and 111 curves cross. The inflection points
I 1
0
are better demonstrated in the field variation of the susceptibility (insert in figure 3) and indicate a metamagnetic transition. Such a transition is also visible in the magnetoresistivity. The inflection points in the M(H) curves are not observed above 3.5 K.
Fig. 3 bgnetization of CeBs per Ce ion versus external magnetic field.
Insert : magnetic field dependence of the a.c. susceptibility.
It is surprising that the 110 .curve
I )
in fi- gure 3 shows a Ce magnetic moment in high fields close to the free ion saturation value (2.14 pB), while Geballe et a1 /I/ find a saturation moment in polycrystalline CeB6 which corroborates the r 7moment (0.71 pB). At present thsi must remain unex- plained. Clearly, further experiments are necessary to improve the understanding of the magnetic beha- vior of CeBs
References
/1/ Matthias,B.T., Geballe, T.H., Andres, K., Corenzwit, E., Hul, G.W., and Maita, J.P., Science
159
(1968) 530.Geballe, T.H., Matthias, B.T., Andres, K., Maita, J.P., Cooper, A.S. and Corenzwit, E., Science
160
(1968) 1443./2/ Nickerson, J.C. and White, R.M., J.Appl.Phys.
40
(1969) 1011 /3/ Winzer, K., Solid State Commun.16
(1975) 521.141 Verhoeven, J.D., Gibson, E.D., Noack, M.A. and Conzemius, R.J. Journal of Crystal Growth
