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

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U3Co4Ge7 and U3Co2Ge7 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. U3Co4Ge7 has a tetragonal structure (I4/mmm), while U3Co2Ge7 crystallizes in en orthorhombic structure (Cmmm), which appears to be a distortion of a tetragonal structure. All measurements document ferromagnetism in U3Co4Ge7 below T_{\text{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. U3Co2Ge7 orders magnetically below 40 K; the magnetic structure is sensitive to the ratio a/c \approx 1, e.g., the deviation from the tetragonal axis.
2012-09-15