Physical properties of Sm3Se4 at low temperatures

Physical properties of Sm3Se4 at low temperatures

Journal of Magnetism and Magnetic Materials 76 & 77 (1988) 117-118 North-Holland, Amsterdam 117 PHYSICAL PROPERTIES OF Sm3Se 4 AT LOW T E M P E R A ...

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Journal of Magnetism and Magnetic Materials 76 & 77 (1988) 117-118 North-Holland, Amsterdam

117

PHYSICAL PROPERTIES OF Sm3Se 4 AT LOW T E M P E R A T U R E S T. F U R U N O *, K. A N D O , S. K U N I I , A. O C H I A I , H. S U Z U K I , M. F U J I O K A * *, T. SUZUKI, W. SASAKI * and T. K A S U Y A Department of Physics, Tohoku University, Sendal 980, Japan • Department of Physics, Tokyo University, Hongo, Tokyo 113, Japan • * Cyclotron and R.1. Center, Tohoku University, Sendai 980, Japan The specific heat of Sm3Se4 was measured between 0.15 and 5 K; it has a broad maximum around 1.2 K and a linear temperature dependence at around the lowest temperature. A ),-value of 4.5 J / m o l K 2 was obtained from this linear part. There are then low lying energy excitations with extremely large density of state in this compound and suggesting the possibility of a heavy fermion state with no free carrier. We checked this point by the measurements of magnetic susceptibility, specific heat and M/3ssbauer effect in a magnetic field to distinguish the possiblity of a spin glass state.

There are still mysteries about the low temperature properties in valence fluctuating material of Th3P 4 type of Sm-chalchogenides [1,2]. One of the problems is a sample preparation to get a good stoichiometry as indicated by Kaldis [3]. The lattice constants of Sm3Se4 were measured to be 8.880 ,~. The molar susceptibility of Sm3Se4 at room temperature is just between those of Sm3Se4 and Sm3S4 of the IBM group [4]. We measured the specific heat of Sm3Se4 at low temperature to elucidate the Schottky-like specific heat anomaly around 1.2 K. The result may be interpreted as the magnetic ordering of the random system [5], as the crystalline electric field effect of the Sm3+ ion or as dense Kondo behavior. The measurements were done by a thermal relaxation method for 0.15 K < T < 1.5 K and by a thermal pulsed method for 1.45 K < T < 3.5 K, and by an adiabatic calorimeter method at T > 2 K and the result is shown in fig. 1. A peak is

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observed at 1.15 K. The Schottky type analysis with two non-degenerate levels fails to fit the experimental results, especially at lower temperature as shown in fig. 2. The specific heat has nearly T-linear dependence at lower temperature (0.15 K < T < 0 . 8 K) with a y value of 4.5 J / m o l K 2. The entropy per Sm 3+ reaches ½ In 2 at T = I K, R In 2 at T = 2 . 4 K and 1.2R In 2 at T = 7 K which is too small to consider the ground state as a F8 quartet but larger than the doublet ground state. However, the excess entropy is well accounted for by the entropy of disorder of the mixture of di- and trivalent Sin. Note that the entropy at 0.15 K was estimated to be 0.05R per Sm 3+ from the extrapolation of the specific heat to lower temperature. To check the origin of the specific peak, we applied magnetic fields of 5 and 10 T above 2 K as shown in fig. 1. Only a small change of the specific heat was observed. To check the possibility of the spin glass type magnetic specific heat at low temperature, we have done the specific heat measurement for 0.15 K < T < 1.5 K under the magnetic field of 10 kOe. It indicated that the specific heat peak shifted to higher temperature by several hundred mK. The specific heat for the lower part of the peak show the parallel shift to higher temperatures. We have done also a Mi3ssbauer effect measurements in a magnetic field of 5 T at low temperature. We did not observe any hyperfine splitting down to 4.2 K even at high magnetic fields of 5 T. But the line width increased slightly, consistent with a weak induced magnetization at low temperature. Fig. 3 shows the susceptibility of Sm3Se4 at low temperature. The susceptibility has a cusp at 0.8

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7C Furuno el al. / Properties of Sm 3Se 4 at low temperatures

heavy fermion. The present results, combined with other experimental results reported already, suggest the following generalized Kondo picture

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without the conduction electrons: The dielectric m e a s u r e m e n t d o n e in o u r g r o u p r e c e n t l y r e v e a l e d t h a t t h e s h o r t r a n g e o r d e r o f di a n d t r i v a l e n t S m o c c u r s a r o u n d r o o m t e m p e r a t u r e g r a d u a l l y . It will be seen the Anderson localization or the glass-like W i g n e r c r y s t a l l i z a t i o n o f t h e n a r r o w 4f b a n d w i t h substantial mixing of conduction electron chara c t e r b e c a u s e t h e 4f level is v e r y n e a r t h e b o t t o m o f t h e c o n d u c t i o n b a n d . T h i s gives t h e K o n d o - l i k e q u e n c h i n g o f t h e m o m e n t as well as t h e l a r g e 7 value and hopping-like conduction with small activation energy, which can be vanishingly small as t h e f u n c t i o n o f f r e q u e n c y . M o r e d e t a i l e d w o r k is d e f i n i t e l y n e e d e d .

K, i.e. at a temperature slightly lower than the specific heat peak position at 1.15 K. The experimental Wilson ratio, X(0)/7(0) is just on the line obtained from other usual types of References

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[1] A. Tamaki, T. Goto, S. Kunii, T. Suzuki, T. Fujimura and T. Kasuya, J. Phys. C 18 (1985} 5849. [2] A. Tamaki, T. Goto, S. Kunii, M. Kasaya, T. Suzuki, T. Fujimura and T. Kasuya, J. Magn. Magn. Mat. 47 & 48 (1985) 469. [3] E. Kaldis, J. Less-Common Metals 76 (1980) 163. [4] J.M.D. Coey, B. Cornut, F. Holtzberg and S. yon Molnar, J. Appl. Phys. 50 (1979) 1923. [5] S. von Molnar, F. Holtzberg, A. Briggs, J. FIouquet and J.L. Tholence, Valence Instabilities eds. P. Wachter and H. Boppart (North-Holland, Amsterdam, 1982) p. 597.