Structure change and spin density distribution in unique magnetically low-anisotropic compound U4Ru7Ge6
U compounds usually exhibit huge magnetocrystalline anisotropy that is born in strong spin-orbit coupling in U ions and together with participation of 5f orbitals in anisotropic covalent bonding. Magnetization data measured on the U4Ru7Ge6 single crystal with ab initio electronic structure calculations reveal a rare exception from the rule. The easy magnetization direction of this cubic ferromagnet (Tc = 7.5 K) is [111] and the anisotropy field between [100] and [111] is ~ 0.2 T. At temperatures below Tc a rhombohedral distortion leading to 2 inequivalent U positions was observed by precise dilatometry and XRPD measurements. Appearance of the distortion is confirmed by the calculations which also predict for each inequivalent position a different U magnetic moment composed of mutually compensating spin and orbital components. Neutron diffraction experiments at D9 and D3 are proposed to address the important issues of physics of U4Ru7Ge6: the precise knowledge of crystal structure above and below Tc, respectively (D9) and details on the size of U magnetic moment at each inequivalent crystallographic position and the role of spin and orbital components (PND experiment at D3).
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VALISKA Michal; FABELO ROSA Oscar Ramon; KLICPERA Milan; SECHOVSKY Vladimir and STUNAULT Anne. (2016). Structure change and spin density distribution in unique magnetically low-anisotropic compound U4Ru7Ge6. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.5-51-516
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