Exchange Interactions in Rare-earth Magnets $A_2$PrO$_3$ ($A$= alkali metals): Revisited

TL;DR

This study reevaluates exchange interactions in $A_2$PrO$_3$ rare-earth magnets, revealing that considering ionic states beyond conventional assumptions suppresses Kitaev interactions, aligning theoretical predictions with experimental results.

Contribution

It introduces a revised analysis of exchange interactions in Pr-based magnets by including ionic states beyond the conventional model, clarifying the dominance of Heisenberg interactions.

Findings

Kitaev interactions are suppressed when considering ionic states beyond the conventional scheme.

The dominance of Heisenberg interactions explains experimental observations.

Revisiting ionic states resolves previous contradictions in magnetic interaction predictions.

Abstract

Rare-earth materials hold promise to realize exotic magnetic states owing to synergy between electron correlations and spin-orbit coupling. Recently, quasi-two-dimensional honeycomb magnets $A_2$PrO$_3$ ($A$ = alkali metals) were predicted to be good candidates for Kitaev quantum spin liquids, as the Kitaev-type bond-dependent anisotropic interactions dominate over bond-independent isotropic Heisenberg ones. However, experimental observations are negative, questioning the energy hierarchy in Pr$^{4+}$ ions assumed in the conjecture on the basis of the conventional Russell-Saunders coupling scheme. We here revisit the exchange interactions in these Pr compounds, by explicitly taking into account the ionic states beyond the assumption. We show that, while increasing the octahedral crystal field splitting, which was assumed to be negligibly small, relative to the spin-orbit coupling, the Kitaev-type interactions are suppressed to be subdominant compared to prevailing Heisenberg ones. Our finding compromises the contradiction as arising from the peculiar ionic state of the high valence Pr$^{4+}$.