Magnetotransport properties of the Kondo lattice YbPd2Si2, evidence for a new phase below 1.4 K

Journal of Magnetism and Magnetic Materials 76 & 77 (1988) 289-290 North-Holland, Amsterdam

289

M A G N E T O T R A N S P O R T PROPERTIES OF THE K O N D O LATTICE YbPdzSiz, EVIDENCE FOR A NEW PHASE BELOW 1.4 K J.M. BROTO, F. GONZALEZ-JIMENEZ *, A. FERT, J. SANCHEZ Laboratoire the Physique des Solides, Universit~ Paris-Sud. F-91405 Orsay, France

M.J. BESNUS and J.P. KAPPLER L.M.S.E.S., 3 rue de l'Universit~, F-67084 Strasbourg, France We study the heavy fermion properties of YbPd2Si 2 by resistivity, Hall effect and magnetoresistance. A new phase is found below 1.4 K.

The compound YbPd2Si 2 is a Kondo system with a moderate heavy fermion (HF) behavior ( y - - 2 0 3 m J / K 2 m o l ) [1-3]. We report our resistivity, Hall effect and magnetoresistance measurements which confirm the H F character and reveal that YbPd2Si 2 develops a new phase below 1.4 K. We have performed our resistance and Hall effect measurements by a classical ac current technique in a dilution refrigerator system [4]. We first describe our experimental results between 1.4 and 300 K. The resistivity is very high ( - 3 7 0 ~2cm) at room temperature and, as in Kondo lattices with coherence effects, drops to relatively small values at low temperatures (see fig. 1). A variation a s T 2 is observed below about 25 K. The magnetoresistance (see fig. 2), is very strong at low temperatures and, for example, exceeds 50% at 4.2 K and 65 kG. This is much more than in normal metals and even more than in most mixed valence and heavy fermion systems. The Hall constant (see fig. 3), rapidly increases as the

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1OK * On sabbatical leave from Departamento de Fisica, Facultad de Ciencias, UCV, Caracas, Vrnu~zrla.

0304-8853/88/$03.50 © Elsevier Science Publishers B.V.

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J.M. Broto et al. / Magnetotranaport properties of the Kondo lattice YbPd ,Si ,

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Fig. 4. Temperature and magnetic field dependence of the normalized resistance below 1.4 K. observed in heavy H F systems [5]. H o w e v e r Y b P d 2 S i 2 does n o t exhibit the usual m a x i m u m of the coherent H F systems a n d r e m a i n s a l m o s t constant between 20 K a n d the lowest temperatures. W h e r e a s the a n o m a l o u s Hall effect is positive in most Ce systems, a negative sign is often o b s e r v e d for Y b systems [6], which is also the case for Y b P d 2Si 2. Below 1.4 K the resistivity d r o p s r a p i d l y : the resistivity, which is almost c o n s t a n t b e t w e e n 1.4 and 10 K, decreases from 50 ~t~2cm at 1.4 K to a b o u t 25 rt~2cm at 100 inK. T h e striking result, shown in fig. 4, is that a weak m a g n e t i c field restores the resistivity at its value at 1.4 K. This strongly suggests that Y b P d 2 S i 2 develops a low t e m p e r a t u r e phase which is u n s t a b l e in relatively small fields. The threshold field is well defined a n d varies between 150 G at 100 m K to zero at 1.4

K. This gives the t r a n s i t i o n line H , . ( T ) represented b y a d o t t e d line in fig. 4 (see in the p l a n e R / R ] . s K = 1). The c o o p e r a t i v e phases d e v e l o p e d in several H F systems at low t e m p e r a t u r e s h a p p e n to be very hard to detect [7,8]. This is the case for the low t e m p e r a t u r e p h a s e o f Y b P d 2 S i 2 : M~Sssbauer e x p e r i m e n t s of 17°yb d o w n to 50 m K [9] do not detect a n y o r d e r i n g of the m a g n e t i c m o m e n t s (taken iv/to a c c o u n t the M/Sssbauer exp e r i m e n t a l accuracy, if a m o m e n t exists it should be smaller than 0.02/LB). In c o n c l u s i o n o u r m e a s u r e m e n t s confirm the heavy fermion b e h a v i o r of Y b P d , S i 2 and reveal the existence of a c o o p e r a t i v e phase below 1.4 K. T h e a b s e n c e of h y p e r f i n e field in the M 6 s s b a u e r e x p e r i m e n t below 1.4 K, suggests that the observed p h a s e arises from weak magnetic correlations present in the F e r m i liquid. The extreme sensitivity to small a p p l i e d m a g n e t i c fields indicates that the low t e m p e r a t u r e p h a s e is one of the m o r e u n s t a b l e even o b s e r v e d in H F systems.

References [11 S.K. Dhar, E.V. Sampathkumaran, R. Vijayaraghavan and R. Kuentzler, Solid State Commun. 61 (1987) 479. [2] P. Bonville and J.A. Hodges, J. Magn. Magn. Mat. 47 & 48 (1985) 152. [3] M.J. Besnus, M. Benakki, A. Braghta and J.P. Kappler, J. Magn. Magn. Mat. 76 & 77 (1988) 471. [4] M. Coussignac, Thesis CNAM Grenoble (1980) and P. Pari, Thesis CNAM Paris (1987). [5] A. Fert, A. Hamzic and P.M. Levy, J. Magn. Magn. Mat. 63 & 64 (1987) 535. [6] E. Cattaneo, Z. Phys. B. CM 64 (1986) 317. [7] G. Aeppli, E. Bucher, C. Broholm, J.K. Kjems, J. Baumann and J. Hufnagl, Phys. Lett. 60 (1988) 615. [8l A. Hamzic and A. Fert, J. Magn. Magn. Mat. 76 & 77 (1988) 221. [9] J.A. Hodges, private communication.