Antiferromagnetic and Orbital Ordering on a Diamond Lattice Near Quantum Criticality

TL;DR

This study uncovers a magnetic ordering transition in FeSc2S4 near quantum criticality, showing how structural changes and pressure influence magnetic states and spectral weight distribution.

Contribution

It reports the first observation of magnetic ordering in FeSc2S4 and explores how pressure affects its magnetic transition and spectral properties near criticality.

Findings

Magnetic ordering occurs at 11.8 K after structural transition.

Pressure reduces the transition temperature to 8.6 K.

Magnetic spectral weight shifts to higher energies under pressure.

Abstract

We present neutron scattering measurements on powder samples of the spinel FeSc2S4 that reveal a previously unobserved magnetic ordering transition occurring at 11.8(2)~K. Magnetic ordering occurs subsequent to a subtle cubic-to-tetragonal structural transition which distorts Fe coordinating sulfur tetrahedra lifting the orbital degeneracy. The application of 1~GPa hydrostatic pressure appears to destabilize this N\'eel state, reducing the transition temperature to 8.6(8)~K and redistributing magnetic spectral weight to higher energies. The relative magnitudes of ordered $\langle m \rangle^2\!=\!3.1(2)$ and fluctuating moments $\langle \delta m \rangle^2\!=\!13(1)$ show that the magnetically ordered ground state of FeSc2S4 is drastically renormalized and in proximity to criticality.