Anomalous Transport and Thermal Properties of the Solid Solutions U_1-xTh_xCu₅M (M = Al, Ga, In and Sn)

Abstract

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 TO = 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-xΤhxCu5M. Only in the case of UCu5In a substantial positive contribution to the magnetoresistance was observed at low temperatures, as for normal antiferromagnets. For the Aland 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 UCu 5 M 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(Ιn1-xGax), though the unit cell is here suppressed with increasing z. Thus, a similar physical picture is reached in all these systems but involving probably different mechanisms.

Magnetoresistivity studies of intermetallic uranium compounds and their impact on the understanding of exhibited phenomena

“…The results of magnetoresistance measurements on the UCu 5 Al polycrystalline sample, have already been partly reported previously, e.g. taken either up to 8 T [48] or 13 T [49]. The temperature dependences of the electrical resistance R (arb.unit) at 0, 6, 10 and 13 T for UCu 5 Al are given in Fig.…”

“…All of them form a class of moderate heavy fermion compounds, with γ(0) around 100-400 mJ/mol K 2 which has recently been studied intensively in Wrocław on poly-and single-crystalline samples [48]. These compounds though display at low temperatures moderately enhanced γ(0)-values, at the same time exhibit magnetic order of the Kondo-reduced magnetic moments.…”

“…Here we will present the MR only for two representatives of this class of ternaries, namely for UCu 5 Al and UFe 5 Sn, although the MR was measured for all the remaining compounds of this stoichiometry (see Ref. [48]). …”

Heavy-fermion characteristics inUCu5Alsingle crystals

“…4,5 Magnetic sus-ceptibility, NMR, specific heat, and electrical resistivity measurements 1,6,7 have revealed that antiferromagnetic ͑AF͒ order sets in below 18 K. The magnetic structure, determined by neutron powder diffraction scattering, is of a sinusoidally modulated type (k ជ ϭ0, 0, 0.55͒ with the amplitude of uranium moments ( ord ϭ1.45 B at 1.4 K͒, parallel to the c axis. 5 Interesting to recall that the Kondo-like behavior of the temperature-dependent electrical resistivity in conjunction with an enhancement of the C p /T ratio has classified UCu 5 Al as a medium heavy-fermion system.…”

Electronic band structure and the X-ray photoemission spectrum of UCu<SUB>5</SUB>In

“…Each of the two lines 4f 5=2 and 4f 7=2 can be decomposed into a highly asymmetric main line and two symmetric satellites at 7.1 and 2.6 eV higher binding energies. The pronounced asymmetry of the main lines is considered to be caused by many-body e ects of the electron±hole interaction in the photoemission process (van Veenendaal et al 1993, Bocquet et al 1995. According to the Doniach±S Ï unjic (1970) theory, the asymmetry of the main line is due to the angular dependence of screening charges in the electron±hole interaction during the photoemission process and is described by a singularity parameter ¬.…”