Liquid-like correlations in single crystalline Y2Mo2O7: an unconventional spin glass

TL;DR

This study investigates the unconventional spin glass behavior of Y2Mo2O7 through single crystal growth and neutron scattering, revealing liquid-like correlations and frozen degeneracy linked to spin-orbital coupling and local lattice distortions.

Contribution

It provides the first single crystal analysis of Y2Mo2O7, uncovering liquid-like magnetic correlations and highlighting the role of spin-orbital coupling and local disorder in its spin glass state.

Findings

Isotropic magnetic diffuse scattering observed below spin glass transition

Failed to model diffuse scattering with simple spin Hamiltonians

Heat capacity shows T^2 dependence indicating frozen degeneracy

Abstract

The spin glass behavior of Y2Mo2O7 has puzzled physicists for nearly three decades. Free of bulk disorder within the resolution of powder diffraction methods, it is thought that this material is a rare realization of a spin glass resulting from weak disorder such as bond disorder or local lattice distortions. Here, we report on the single crystal growth of Y2Mo2O7. Using neutron scattering, we present unique isotropic magnetic diffuse scattering arising beneath the spin glass transition despite having a well-ordered structure at the bulk level. Despite our attempts to model the diffuse scattering using a computationally exhaustive search of a class of simple spin Hamiltonians, we were unable to replicate the experimentally observed energy-integrated (diffuse) neutron scattering. A T^2-temperature dependence in the heat capacity and density functional theory calculations hint at significant frozen degeneracy in both the spin and orbital degrees of freedom resulting from spin-orbital coupling (Kugel-Khomskii type) and random fluctuations in the Mo environment at the local level.