Effect of pressure on the electrical resistivity of CePtGa

ELSEVIER

Physica B 206 & 207 (1995) 199-201

Effect of pressure on the electrical resistivity of CePtGa Y. Uwatoko a'*, T. Ishii a, G. Oomi a, S.K.

Malik b

aDepartment of Physics, Faculty of General Education, Kumamoto University, Kumamoto 860, Japan bTata Institute of Fundamental Research, Homi Bhabha Road, Coraba, Bombay 400 005, India

Abstract

Electrical resistivity p(T) and the magnetoresistance (MR) of CePtGa have been measured under high pressure up to 2 GPa. It is found that the N6el temperature TN decreases with increasing pressure and disappears above 1 GPa. MR at 4.2 K is negative showing an H2-dependence. The magnitude of the HLcoefficient A decreases with increasing pressure having the rate of dlAI/dP = -6.4 × 10 4 T-2 GPa 1.

Recently, Ce-based ternary compounds have been studied extensively because of their anomalous physical properties such as heavy fermion behavior, Kondo effect, valence fluctuation, metal-insulator transition and so forth [1,2]. These properties are considered to arise from the hybridization between localised 4f electrons and conduction electrons. Since the hybridization strength Vcf of Ce-based compounds is enhanced by an application of pressure, these compounds show a wide variety of physical properties under high pressure. A n equiatomic ternary compound CePtGa has the orthorhombic TiNiSi-type structure and is a Kondo compound showing antiferromagnetic order with N6ei temperature T N = 3.5K. In this work, we present the results of measurements of the electrical resistivity and magnetoresistance at 4.2 K under high pressure up to 2 GPa in order to obtain information about the electron correlation in this ternary compound. A polycrystalline sample of CePtGa was prepared by arc melting in a purified argon atmosphere. Hydrostatic pressure up to 2 GPa was generated using a C u - B e piston-cylinder device of a 1:1 mixture of Fluorinert, FC 70 and 77 as a pressure transmitting

* Corresponding author.

medium. The pressure was kept constant by means of controlling the load within +-1% throughout the measurement. Electrical resistivity was measured in the temperature range from 2 K to 300 K by a standard DC four-probe technique. The temperature was determined by a calibrated Cu(Fe0.07%)-Chromel thermocouple above 4.2 K and a calibrated carbonglass below 4.2 K. The transverse magnetoresistance at 4.2 K was measured up to 5 T using a superconducting magnet. Fig. 1 shows the temperature dependence of electrical resistivity p(T) at various pressures. At P = 0 GPa, p(T) was found to have a maximum around T = 3.4 K which corresponds to antiferromagnetic ordering. The ordering temperature TN was in good agreement with the previous value [3]. Above 3.4 K, p(T) decreases with increasing temperature until it has a minimum around 24 K, and then increases with a broad shoulder around 100 K. The temperature dependence of p(T) was similar to that of a typical concentrated Kondo compound CeA12 [4]. p(T) increases with increasing pressure as a whole, while that of P = 1.5 GPa exhibits a broad maximum around 80 K and then this maximum is enhanced by pressure. Fig. 2 shows p(T) in the low temperature region (T < 50 K) at various pressures. The N6el temperature TN is defined as the temperature where the p(T) curve shows a peak. Tr~ (shown by arrows in Fig. 2)

0921-4526/95/$09.50 (~) 1995 Elsevier Science B.V. All rights reserved SSD1 0921-4526(94)00407-2

200

Y. Uwatoko et al. / Physica B 206 & 207 (1995) 199-201 4

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Fig. 1. Electrical resistivity p(T) of CePtGa as a function of temperature under various pressures.

Fig. 3. N6el temperature T N of CePtGa as a function of pressure. The solid curve is a guide to the eye.

d e c r e a s e s with increasing pressure a n d a b o v e 0.8 G P a is n o t o b s e r v e d d o w n to 2 K. A m a x i m u m in the p(T) c u r v e is f o u n d a r o u n d 6 K at P = 2 G P a . This origin is n o t clear, but we suggest that this c o r r e s p o n d s to the resistivity m a x i m u m d u e to t h e K o n d o effect since the K o n d o t e m p e r a t u r e (TK) increases with increasing p r e s s u r e [5]. T h e pressure d e p e n d e n c e of T N is s h o w n in Fig. 3. T N d e c r e a s e s with increasing pressure in a n o n - l i n e a r fashion o b s e r v e d in C e I n 3 [6] or U G e 2 [7]. T N seems

to d i s a p p e a r a b o v e 1 G P a . We o b t a i n e d a m a g n i t u d e of pressure derivative d T N / d P = - 0 . 7 K / G P a at P = 0 GPa. Fig. 4 shows the t r a n s v e r s e m a g n e t o r e s i s t a n c e ( M R ) at 4.2 K u n d e r various pressures. A t P = 0 G P a , t h e M R ratio Ap/p(O) = [ p ( H ) - p(O)]/p(O) is a b o u t - 5 % at H -- 5 T. T h e negative M R is a characteristic of a n i n c o h e r e n t K o n d o system [8]. T h e value of the M R ratio at 5 T is s u p p r e s s e d by p r e s s u r e , b u t its sign r e m a i n s negative up to 2 G P a . T h e H 2 coefficient A decreases linearly with increasing p r e s s u r e h a v i n g t h e rate of dlA[/dP = - 6 . 4 x 10 - 4 T 2 G P a 1 as s h o w n in Fig. 5. T h e coefficient A seems to b e positive a b o v e 3 G P a , h e n c e C e P t G a is e x p e c t e d to show a crossover from i n c o h e r e n t K o n d o state a r o u n d 3 G P a . W e also m e a s u r e d M R at 2 K. T h e whole b e h a v i o r is similar to

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Fig. 2. Temperature dependence of p at low temperature under various pressures. N6el temperature T N is shown by an arrow.

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Y. Uwatoko et al. / Physica B 206 & 207 (1995) 199-201

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pressure. Tr~ decreases with increasing pressure at the rate of dT~/dPle=o = - 0 . 7 K / G P a and disappears near 1 GPa. A t 2 GPa, p ( T ) exhibits two maxima around 6 K and 80 K. The M R ratio at 4.2 K shows H2-dependence. The H 2 coefficient A decreases linearly with increasing pressure at the rate of dial/ d P = - 6 . 4 × 10 -4 T -2 G P a -1.

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Fig. 5. MR at 4.2K as a function of H 2 under various pressures, and the pressure dependence of the H 2 coefficient of the magnetoresistance A at 4.2 K. The solid curves show the result of least-squares fit. that at 4 . 2 K . The pressure derivative of the H 2 coefficient d l A l / d P is the same as the value at 4.2 K. In conclusion, we have reported the electrical resistivity and magnetoresistance for C e P t G a under high

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