Magnetic and transport properties of UBi₂ and USb₂ single crystals

Abstract

The thermoelectric power, S(T), of USb₂ and UBi₂, which are tetragonal, uniaxial antiferromagnets below T _N = 202 K and 180.8 K, respectively, have been examined between 0.4 K and 300 K. The values of S(T), up to now known above 70 K for USb₂ and unknown for UBi₂, are positive along the a-axis for both compounds in the whole examined temperature range. The S(T) data for the c-axis (the easy magnetization axis) are positive near room temperature for USb₂ and UBi₂ but 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 composed 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 corresponding minima although less pronounced than those in USb₂. Having at disposal the highest purity single crystals in comparison to those for which the resistivity, ρ(T), has been reported in literature, the ρ(T) anisotropy was re-examined for these two systems. Magnon and phonon contributions to their total electrical resistivity have been determined and the critical fluctuation behaviour of the resistivity near T _N for both dipnictides has 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.

Acknowledgements

Special thanks are expressed to Prof. Z. Henkie for helpful discussions and allowing the use of his samples. The author is also grateful to Prof. R. Troć and Dr. P. Wiśniewski for their critical reading the manuscript and M.Sc. R. Gorzelniak for his help in the magnetic susceptibility measurements. The Polish Committee for Scientific Research, Grant No. 1 P03B 073 27, supported this work.