The $3d$-Electron Heisenberg Pyrochlore Mn$_2$Sb$_2$O$_7$

TL;DR

This study investigates the magnetic properties of the rare Heisenberg pyrochlore Mn₂Sb₂O₇, revealing a spin-glass transition at low temperature and highlighting the significance of low spin-orbit coupling in 3d transition metal pyrochlores.

Contribution

It demonstrates that Mn₂Sb₂O₇ is an extremely rare Heisenberg pyrochlore with a spin-glass ground state, emphasizing the role of low spin-orbit coupling in 3d pyrochlores.

Findings

Spin-glass transition at 5.5K observed.

Disorder from Mn vacancies suppresses the transition.

Low spin-orbit coupling makes Heisenberg pyrochlores more accessible.

Abstract

In frustrated magnetic systems, geometric constraints or the competition amongst interactions introduce extremely high degeneracy and prevent the system from readily selecting a low-temperature ground state. The most frustrated known spin arrangement is on the pyrochlore lattice, but nearly all magnetic pyrochlores have unquenched orbital angular momentum, constraining the spin directions through spin-orbit coupling. Pyrochlore Mn$_2$Sb$_2$O$_7$ is an extremely rare Heisenberg pyrochlore system, with directionally-unconstrained spins and low chemical disorder. We show that it undergoes a spin-glass transition at 5.5K, which is suppressed by disorder arising from Mn vacancies, indicating this ground state to be a direct consequence of the spins' interactions. The striking similarities to $3d$ transition metal pyrochlores with unquenched angular momentum suggests that the low spin-orbit coupling in the $3d$ block makes Heisenberg pyrochlores far more accessible than previously imagined.