Synthesis and magnetic studies of ternary germanides U 3 Co 4 Ge 7 and U 3 Co 2 Ge 7

Abstract

U 3 Co 4 Ge 7 and U 3 Co 2 Ge 7 have been prepared as single crystals by solution growth from tin flux. U 3 Co 4 Ge 7 crystallizes in the tetragonal structure (I4/mmm) with lattice parameters a = 0,4116 nm and c = 2,749 nm and U 3 Co 2 Ge 7 possesses the orthorhombic structure (Cmmm) with a = 0,4151 nm, b = 2,498 nm, c = 0,4160 nm. All measurements document ferromagnetism in U 3 Co 4 Ge 7 below T C = 21 K. The magnetization and magnetic susceptibility measurements revealed strong magnetocrystalline anisotropy. The c-axis has a strong ferromagnetic contribution to the magnetization and was found to be the easy-magnetization direction. U 3 Co 2 Ge 7 shows onset of magnetic ordering at 41 K. The b-axis is the easy magnetization direction with the saturated magnetization μ sat = 1 μ B /U at 2 K. The magnetization curves show anomalous behavior; the virgin curve goes far out of the hysteresis loop and reaches higher value of saturated magnetization.