Lattice anisotropy in uranium ternary compounds: UTX

Abstract

a b s t r a c tSeveral U-based intermetallic compounds (UCoGe, UNiGe with the TiNiSi structure type and UNiAl with the ZrNiAl structure type) and their hydrides were studied from the point of view of compressibility and thermal expansion. Confronted with existing data for the compounds with the ZrNiAl structure type a common pattern emerges. The direction of the U-U bonds with participation of the 5f states is distinctly the "soft" crystallographic direction, exhibiting also the highest coefficient of linear thermal expansion. The finding leads to an apparent paradox: the closer the U atoms are together in a particular direction the better they can be additionally compressed together by applied hydrostatic pressure.

Magnetism and hydrogen absorption in UNiZn

“…The switchover of the nearest U-U spacing from a to the c-axis due to hydrogenation should switch also the easy compressible direction to c, if the U-U bond direction matters. As it was later indeed observed experimentally, it strongly corroborates the anisotropy concept, which could be even applied to magnetic anisotropy, exhibiting the easy magnetization direction perpendicular to the nearest U-U links [24]. Unfortunately, no details of magnetic structure of UNiAlD 2.1 could be determined so far [12].…”

Magnetic anisotropy in uranium monosulfide probed by magnetic torque measurements

“…Anisotropic behaviors have been observed in various cubic 4f and 5f electron-based materials [1][2][3][4][5]. The main source of anisotropy in these materials is magnetocrystalline anisotropy, which involves large orbital magnetic moment, strong spin-orbit coupling, and hybridization of 5f -electrons with p, d-states of ligand ions [6][7][8][9][10][11][12]. This is well emphasized in uranium monosulfide, in which the largest magneto-crystalline anisotropy has been observed for cubic systems [13,14].…”

Structural and electronic response of U3Fe4Ge4 to high pressure

“…In orthorhombic UCoGe, the U atoms are also coordinated in zig-zag chains along the a direction where d U-U is also shortest and that manifests itself as the softest direction. 15 The individual isothermal linear compressibilities can be used to express the isothermal bulk modulus through the relation B 0 ¼ 1/k V , where k V is the volume compressibility which for the orthorhombic unit cell is given by k V ¼ k a þ k b þ k c . For U 3 Fe 4 Ge 4 , these calculations resulted in k V ¼ 0.007 GPa À1 and B 0 ¼ 143 GPa.…”

“…Due to the strong spin-orbit interaction, the U magnetic moments are aligned perpendicular to the bonding direction. 13 Such situation was disclosed for U compounds where a pronounced bonding directionality could be determined, as for those belonging to the ZrNiAl isotype (hexagonal), 14 the TiNiSi structure type (orthorhombic) 15 and for the ternary C14 Laves phase U 2 Fe 3 Ge. 9 Recently, a novel itinerant ferromagnet U 3 Fe 4 Ge 4 was characterized.…”