Spin-lattice instability to a fractional magnetization state in the spinel HgCr2O4

TL;DR

This study investigates the spin-lattice transition in the frustrated spinel HgCr2O4 under magnetic field, revealing a phase change to a fractional spin state with lattice symmetry alteration, using neutron and X-ray scattering.

Contribution

It provides the first detailed microscopic characterization of the fractional magnetization state and its associated lattice distortion in HgCr2O4.

Findings

Phase transition at ~10 Tesla from canted Neel to fractional spin state.

Correspondence between spin state and lattice symmetry change.

Identification of a fractional spin state with S/2 in HgCr2O4.

Abstract

Magnetic systems are fertile ground for the emergence of exotic states when the magnetic interactions cannot be satisfied simultaneously due to the topology of the lattice - a situation known as geometrical frustration. Spinels, AB2O4, can realize the most highly frustrated network of corner-sharing tetrahedra. Several novel states have been discovered in spinels, such as composite spin clusters and novel charge-ordered states. Here we use neutron and synchrotron X-ray scattering to characterize the fractional magnetization state of HgCr2O4 under an external magnetic field, H. When the field is applied in its Neel ground state, a phase transition occurs at H ~ 10 Tesla at which each tetrahedron changes from a canted Neel state to a fractional spin state with the total spin, Stet, of S/2 and the lattice undergoes orthorhombic to cubic symmetry change. Our results provide the microscopic one-to-one correspondence between the spin state and the lattice distortion.