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Submitted on 1 Jan 1971
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EFFECT OF SPIN-ORBIT SCATTERING ON THE SUPERCONDUCTING Tc AND SUSCEPTIBILITY
OF La : Ce ALLOYS
A. Edelstein, J. Jackson, D. Bardos
To cite this version:
A. Edelstein, J. Jackson, D. Bardos. EFFECT OF SPIN-ORBIT SCATTERING ON THE SUPER- CONDUCTING Tc AND SUSCEPTIBILITY OF La : Ce ALLOYS. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-219-C1-220. �10.1051/jphyscol:1971169�. �jpa-00214496�
JOURNAL DE PHYSIQUE Colloque C I, supplkment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1 - 219
EFFECT OF SPIN-ORBIT SCATTERING ON THE SUPERCONDUCTING T,
AND SUSCEPTIBILITY OF La : Ce ALLOYS (*) A. S. EDELSTEIN
Department of Physics, University of Illinois, Chicago, Illinois 60680 and Argonne National Laboratory, Argonne, Illinois 60439
and J. E. JACKSON
Department of Physics, University of Illinois, Chicago, Illinois 60680 and D. I. BARDOS (**)
Argonne National Laboratory, Argonne, Illinois 60439
Rbsumb. - On montre que I'addition de Th, qui cause une forte dispersion spin-orbite, n'influence pas la variation de Tc dans le La, provoquke par 1 at. % de Ce. Le moment de Kondo par gramme de Ce a une dkpendance en fonction de la tempkratu~e en BT-112, ou B est indkpendant de la concentration de Th. Le moment des autres impuretks suit une dkpen- dance en AIT, ob A dkcroit d'un facteur trois pour I'addition de 4 at. % de Th.
Abstract. - It is shown that the addition of Th which causes strong spin-orbit scattering does not affect the change in Tc of La caused by 1 at. % Ce. The Kondo moment per gram Ce also follows a BT-112 temperature dependence where B is independent of Th concentration. The moment of other impurities follows an A / T temperature dependence where A decreases a factor of three on the addition of 4 at. % Th.
Gainon and Heeger [I] showed that the addition of an impurity such as Pt which causes strong spin-orbit scattering suppresses the Kondo effect in Cu : Mn alloys.
Garland et al. [2] interpreted this effect as due to a spin relaxation time mechanism.
Here we report measurements of the effects of adding Th which causes strong spin-orbit scattering in La : Ce alloys on the superconducting T, and suscep- tibilities of these alloys. Sugawara and Eguchi [3] first reported the observation of a Kondo effect in La : Ce alloys. We are currently investigating the effect of the addition of Th on the resistivity of these alloys.
Matthias et al. [4] showed that the addition of Ce has an anomalously large effect upon the supercon- ducting transition temperature T, of La. Tunneling 151 and specific heat measurements [6] established the existence of a large number of states in the energy gap.
These effects are connected with the fact that these alloys also exhibit a Kondo effect. Hence it is interes- ting to see how the superconducting transition tem- perature Tc is affected by the addition of Th which causes strong spin-orbit scattering. We have measured T, for fcc Ce,.,, Th, La ,.,,-, (x = 0,0.005,0.01,0.04, 0.06) alloys and found that the To decreased linearly with x. One sees in figure 1, that the amount of this decrease is essentially the same as that caused by the addition of Th to La [7]. This implies that the change in T, caused by the addition of the Ce is unaffected by the Th. One might have expected the T, to increase jf the Kondo effect is being suppressed. The points at zero Th concentration which are much lower than the others were taken on samples that were less pure.
(*) Based on work performed in part under the auspices of the U. S. Atomic Energy Commission.
(**) Present address: Fort Wayne Metals Inc., 3211 McAr- thur Drive, Fort Wayne, Indiana 46809.
FIG. 1. - Superconducting TC versus concentration for fcc Ceo.olThz Lao.!+% and Thz Lal.oo-~ alloys.
Susceptibility measurements [8] on La : Ce alloys containing from 2 to 20at. % Ce showed that the suscep- tibility followed a T-% temperature dependence below approximately 50 OK. We have measured the effect of the addition of Th on the susceptibility. A small temperature-independent ferromagnetic impurity con- tribution was subtracted from the susceptibility. The resulting susceptibility for 100 OK 5 T 5 300 fitted the form X, + C/T where X, is temperature independent.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971169
C 1 - 220 A. S. EDELSTEIN AND J. E. JACKSON AND D. I. BARDOS This permitted the subtraction of X , for the suscepti-
bility. The value of X, was nearly the same for all the samples. The remaining susceptibility at low tempera- tures was fitted to an equation of the form AIT + BIT%.
This fit is based on the model that the A term results from the Curie law behavior of impurities other than the Ce while the B term is the Kondo contribution of the Ce. To test this model we plot in figure 2, XT'/2 vs T-%.
One sees that the corrected data for the three samples fits straight lines when plotted in this manner. There are two interesting things to note. First the intercept on the T - % = 0 axis, which represents B, is constant for all these samples and equal to the value obtained for the higher concentration La : Ce samples of Ref. 8.
Hence, the Kondo susceptibility is unaffected by the addition of the Th. Secondly the A term which is the contribution of the other impurities is drastically reduced. This is probably the effect of spin-orbit scattering quenching the moment as first observed by Wohlleben and Luo [9]. We are investigating which impurity is responsible for the A term. The same sam- ples that were used in the susceptibility measurements were among those used in the T, measurements.
These samples gave results which deviated from the
others only for low Th concentrations before the A contribution was quenched.
t m
. $ 8 -
N HIGHER CONCENTRATION
. F L ~ : c ~ ALLOYS
CeO,O1 Thx L o 0 , 9 9 - ~ X SYMBOL SLOPE INTERCEPT
0.00 11.4
0.01 X 7.4
0.04 4.5 6.5
2
0 0.1 0.2 0 3 0 4 0 5 0.6 0.7
T -112
FIG. 2. - xTlf2 versus T-'12 for several Ce o.o~Thx La 0.99-x
alloys. The susceptibility is normalizedper gram Ce. Also shown are results for high concentration La : Ce samples from Ref. 8.
References
[I] GAINON (D.) and HEEGER (A. J.), Phys. Rev. Letters, [5] EDELSTEIN (A. S.), Phys. Rev., 1969, 180, 505.
1969, 22, 1420. [6] CULBERT (H. V.) and EDELSTEIN (A. S.), Solid State [2] GARLAND (J. W.), BENNEMANN (K. H.), RON (A.), and Comm., 1970, 8, 445.
EDEL~TEIN (A. S-), J. APIJ~. Phys.7 1970, 41,1148. 171 H~~~ (H. H.J et a ~ . , private communication.
[3] SUGAWARA (T.) and EG-UCHI (H.), J . Phys. Soc. fapan,
1966, 21, 725. [8] EDELSTEIN (A. S.), Phys. Rev. Letters, 1968, 20, 1348.
[4] MATTHIAS (B. T.), SUHL (H.) and CORENZWIT (E.), [9] WOHLLEBEN (D.) and Luo (& L.), Phys. Rev. Letters, Phys. Rev. Letters, 1958, 1, 92. 1969, 22, 842.
