H. Fjellvaag | Searcharxiv

arXiv2002

Antiferromagnetic vs ferromagnetic interactions and spin-glass-like behavior in ruthenates

We have made a series of gradient-corrected relativistic full-potential density-functional calculation for Ca-substituted and hole-doped SrRuO$_3$ in para, ferro, and $A$-, $C$-, and $G$-type antiferromagnetic states. Magnetic phase-diagram data for Sr$_{1-x}$Ca$_x$RuO$_3$ at 0 K are presented. Neutron diffraction measurement combined with total energy calculations show that spin-glass behavior with short-range antiferromagnetic interactions rules in CaRuO$_3$. The substitution of Sr by Ca in SrRuO$_3$ decreases the ferromagnetic interaction and enhances the $G$-type antiferromagnetic interaction; the $G$-AF state is found to stabilize around $x$ = 0.75 consistent with experimental observations. Inclusion of spin-orbit coupling is found to be important in order to arrive at the correct magnetic ground state in ruthenates.

cond-mat.mtrl-sci↗

arXiv2002

Violation of the Minimum H-H Separation "Rule" for Metal Hydrides

Using gradient-corrected, all-electron, full-potential, density-functional calculations, including structural relaxations, it is found that the metal hydrides $RT$InH$_{1.333}$ (R = La, Ce, Pr, or Nd; T = Ni, Pd, or Pt) possess unusually short H-H separations. The most extreme value (1.454 Å) ever obtained for metal hydrides occurs for LaPtInH$_{1.333}$. This finding violates the empirical rule for metal hydrides, which states that the minimum H-H separation is 2 Å. Electronic structure, charge density, charge transfer, and electron localization function analyses on $RT$InH$_{1.333}$ show dominant metallic bonding with a non-negligible ionic component between T and H, the H-H interaction beingweakly metallic. The paired, localized, and bosonic nature of the electron distribution at the H siteare polarized towards La and In which reduces the repulsive interaction between negatively charged H atoms. This could explain the unusually short H-H separation in these materials. Also, R-R interactions contribute to shielding of the repulsive interactions between the H atoms.

cond-mat.mtrl-sci↗