Anomalous Transport and Thermal Properties of the Solid Solutions U1-xThxCu5M (M = Al, Ga, In and Sn)

R. Troć, V.H. Tran, D. Kaczorowski and A. Czopnik W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław, Poland

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UCu5M-type compounds are moderate heavy fermion systems with an antiferromagnetic order below TN=18, 16-25, and 25 K for M = Al, (Ga, In), and In, respectively, and a ferrimagnetic order with TC= 54 K for M = Sn. We present the results of magnetoresistance measurements as a function of temperature and applied magnetic field for the pure compounds and for their solid solutions containing Th, i.e. U1-xThxCu5M. Only in the case of UCu5In a substantial positive contribution to the magnetoresistance was observed at low temperatures, as for normal antiferromagnets. For the Al- and Sn-based alloys the magnetoresistance at low temperatures is negative, and its field variation proves the existence of Kondo-type interactions. On Th-substitution the magnetic phase transition is shifted to lower temperature and simultaneously the magnetoresistance becomes less negative. The field dependence of the magnetoresistance of these alloys can be well described by the Coqblin-Schrieffer model. Interestingly, the heat capacity measurements have revealed a general tendency to increase the linear coefficient γ with magnetic dilution of a given UCu5M compound by Th-substitution. This feature reflects an enlargement of the effective mass of conduction electrons with the increase in both the unit cell volume and magnetic dilution. Such a tendency is also observed for the system UCu5(In1-xGax), though the unit cell is here suppressed with increasing x. Thus, a similar physical picture is reached in all these systems but involving probably different mechanisms.

DOI: 10.12693/APhysPolA.97.25 PACS numbers: 75.30.Mb, 72.15.Qm, 75.20.Hr