- Michal Vališka: Detailed study of weakly anisotropic uranium intermetallic U4Ru7Ge6
- 18. 11. 2015, 14:50
- lecture room F2, first floor Ke Karlovu 5
- more information
Abstract:
Uranium intermetallic compounds usually exhibit strong magnetocrystalline anisotropy which is connected with strong spin-orbit coupling in U ions. Our magnetization study of high quality single crystals of U4Ru7Ge6 revealed that this cubic system is a rare exception among this family. This compound was found ordering ferromagnetically below 7.5 K with the easy magnetization axis along the [111] direction. The magnetocrystalline anisotropy, however, appears to be exceptionally weak. The anisotropy energies for the [110] and [100] directions are of the order of µeV. Such low anisotropy is unique in U compounds.
To understand the results better first-principle calculations were performed. A total magnetic moment of 1.00 µB/f.u. has been calculated which is in very good agreement with experimental data. The DFT calculations provide estimation of the spin and orbital components of the magnetic moment at U ions. The relativistic spin-orbit coupling splits the crystallographically equivalent U positions in two types. The U ions at the first site bear almost negligible magnetic moment due to the mutual cancelation of the spin and orbital components. The U magnetic moment at the other type of site than dominate the total moment.
Thermal expansion measurements show negligible length change along the [111] direction and large positive response along [100]. Evolution of the magnetostriction below TC will be discussed.
AC susceptibility measurements of the U4Ru7Ge6 crystal under hydrostatic pressure were also done. A rapid decrease of the ordering temperature was observed with critical pressure for ferromagnetism of ∼ 1.75 GPa derived from the TC value extrapolated to 0 K.