Magnetic and transport properties of UBi2 and USb2 single crystals
Résumé
ABSTRACT Thermoelectric power, S(T), of USb2 and UBi2 that are tetragonal, uniaxial antiferromagnets below TN = 202 K and 180.8 K, respectively, have been examined between 0.4 K and 300 K. The S(T) dependencies, up to now known above 70 K for USb2 and unknown for UBi2, are along the a-axis positive for both compounds in the whole examined temperature range. The S(T) data for the c-axis (the easy magnetisation axis) are positive near the room temperature for USb2 and UBi2 and becomes negative below 120 K and 170 K, respectively, with two very deep minima in S(T) dependence for USb2. In the latter compound the Fermi surface, known from literature, is compose of the only cylindrical sheets that are slightly corrugated and parallel to the c-axis. UBi2, the Fermi surface of which is composed of one spherical and two cylindrical sheets shows the corresponding minima to be less pronounced than those in USb2. Having in disposal the highest purity single crystals in comparison to those for which the resistivity, ρ(T), has been reported in literature up to now, the ρ(T) anisotropy could be re-examined for these two systems. Magnon and phonon contributions to their total electrical resistivity have been determined and critical fluctuation behaviour of the resistivity near TN for both dipnictides hasve also been analysed. Although the magnetic susceptibilities of UBi2 and USb2 reveal a similarity, their transport properties are significantly different due to the difference in the Fermi surface topology.
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