Magnetic Studies of Ternary Germanides U3Co4Ge7 and U3Co2Ge7 with Strong Uniaxial Anisotropy

Abstract

U 3 Co 4 Ge 7 and U 3 Co 2 Ge 7 have been prepared as single crystals by the solution growth method from tin flux and studied by X-ray diffraction, magnetic, transport, and specific-heat measurements; ab initio electronic-structure calculations have also been performed to study magnetism theoretically. U 3 Co 4 Ge 7 has a tetragonal structure ( I 4/ m m m ), while U 3 Co 2 Ge 7 crystallizes in en orthorhombic structure ( C m m m ), which appears to be a distortion of a tetragonal structure. All measurements document ferromagnetism in U 3 Co 4 Ge 7 below T C = 21 K with a strong magnetocrystalline anisotropy. The c -axis has a strong ferromagnetic contribution to magnetization and was found to be the easy-magnetization direction. U 3 Co 2 Ge 7 orders magnetically below 40 K; the magnetic structure is sensitive to the ratio a / c ≈1, e.g., the deviation from the tetragonal axis.