Magnetic correlations and structure in bixbyite across the spin-glass transition

Abstract

Magnetic frustration in atomically ordered crystals gives rise to a broad range of quantum phenomena. The mineral bixbyite, $\mathrm{F}{\mathrm{e}}_{2\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}{\mathrm{O}}_{3}$, has magnetic frustration induced by atomic disorder. The end-members $\mathrm{M}{\mathrm{n}}_{2}{\mathrm{O}}_{3}$ and $\ensuremath{\beta}\ensuremath{-}\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{3}$ both have magnetically ordered ground states, but the bixbyite crystal studied here, with a composition $\mathrm{F}{\mathrm{e}}_{1.12}\mathrm{M}{\mathrm{n}}_{0.88}{\mathrm{O}}_{3}$, instead undergoes a spin-glass-like transition near 32 K. In this study, the magnetic correlations and atomic structure of bixbyite are followed across the spin-glass transition using powder and single-crystal neutron scattering. Refinement of Bragg intensities from neutron diffraction data allows precise determination of the average Fe and Mn concentration on the different crystallographic sites of the structure. No structural transitions occur in bixbyite upon cooling. Using the three-dimensional magnetic difference pair distribution function (3D-m\ensuremath{\Delta}PDF), the magnetic correlations are resolved spatially and their temperature dependence determined. The results demonstrate that the spin-spin correlations are strong well above the glass transition temperature, consistent with the spin-glass nature of the magnetism in bixbyite.