Crystal Structure and Physical Properties of Uranium–Copper Oxyphosphide UCuPO

Abstract

Single crystals of uranium- and thorium-copper oxyphosphide, UCuPO and ThCuPO, have been grown by an iode-transport method. The crystallographic parameters for UCuPO and ThCuPO are determined at room temperature by single crystal X-ray diffraction. These materials crystallize in a tetragonal ZrCuSiAs-type structure. UCuPO is confirmed to be a semimetallic antiferromagnet with a Neel temperature of T N = 220 K, while ThCuPO shows non-magnetic metallic behavior. The specific heat measurements at temperatures much lower than T N indicate that the density of states (DOS) for both compounds is quite low, and that the 5 f component of DOS is fully gapped due to antiferromagnetic ordering in UCuPO. The magnetic susceptibility for a single crystal of UCuPO shows a large uniaxial anisotropy along the c axis in the paramagnetic state. The resistivity measurements for UCuPO under high pressures up to 2.45 GPa indicate a slight increase of the Neel temperature. When compared with the data for the reference material T...