Calculation of Multipolar Exchange Interactions in Spin-Orbital Coupled Systems

Abstract

A new method of computing multipolar exchange interaction in spin-orbit coupled systems is developed using multipolar tensor expansion of the density matrix in local density approximation+U electronic structure calculation. Within the mean field approximation, exchange constants can be mapped into a series of total energy calculations by the pair-flip approximation technique. The application to uranium dioxide shows an antiferromagnetic superexchange coupling in dipoles but a ferromagnetic one in quadrupoles which is very different from past studies. Further calculation of the spin-lattice interaction indicates it is of the same order with the superexchange and characterizes the overall behavior of the quadrupolar part as a competition between them.

Hidden order and multipolar exchange striction in a correlated f -electron system

“…Therefore, as has been previously noted (8,25), extracting a full superexchange Hamiltonian of NpO2 from experimental (e.g., INS) data is virtually impossible due to a large number of parameters entering into the fit of an excitation spectra. The same difficulty is encountered by ab initio approaches based on total energy calculations for symmetry broken phases (15,33,43), which require a large number of very precises calculations to extract multiple nonnegligible matrix elements ofV , with the magnitude of 0.5 meV and above. Within the present framework, all interactions are extracted from a single ab initio calculation for paramagnetic NpO2.…”

Spin-orbital entangled molecular jeff states in lacunar spinel compounds

“…The j eff ¼ 3/2 systems in the strong coupling limit could also have a significant implication in terms of unconventional multipolar orders [38][39][40] . On top of the nonmagnetic insulating behaviour, the weak tetragonal superstructure and the anomalous magnetic response observed in GaNb 4 S 8 at TB31 K 41 could give some clues on the quadrupolar ordered phase as well as the spin liquid phase suggested in ref.…”

Unraveling 5f-6d hybridization in uranium compounds via spin-resolved L-edge spectroscopy

“…However, a method to directly and selectively probe the electronic 5 f , 6 d states and their hybridization has not been available yet, which, in turn, is crucial for a comprehensive understanding of the unconventional mechanisms that regulate the physics of 5 f electrons in actinides. In addition, with the intrinsic dificulties handling actinide elements due to their toxic and radioactive nature, theoretical work on actinide compounds has been much more extensive than experimental work 3 , 13 , 15 , 16 . Therefore the need for a technique capable of directly probing the relevant electronic states, as well as testing theoretical predictions, is abundantly clear.…”