Glassy freezing of orbital dynamics in FeCr2S4 and FeSc2S4

TL;DR

This study investigates the glass-like freezing of orbital reorientation dynamics in FeCr2S4 and FeSc2S4, revealing a continuous slowdown of orbital relaxation that transitions to quantum tunneling at low temperatures.

Contribution

It provides a detailed dielectric analysis of orbital glass transition in sulpho-spinels, highlighting the coupling with lattice and the quantum tunneling effects at low temperatures.

Findings

Orbital reorientations exhibit relaxational behavior detectable via dielectric permittivity.

Orbital relaxation slows down over six decades in time before quantum tunneling suppresses the glass transition.

Contact contributions and conductivity are accounted for in the dielectric spectra analysis.

Abstract

We report on a thorough dielectric investigation of the glass-like freezing of the orbital reorientation-dynamics, recently found for the crystalline sulpho-spinels FeCr2S4 and FeSc2S4. As the orbital reorientations are coupled to a rearrangement of the surrounding ionic lattice via the Jahn-Teller effect, the freezing of the orbital moments is revealed by a relaxational behaviour of the complex dielectric permittivity. Additional conductivity (both dc and ac) and contact contributions showing up in the spectra are taken into account by an equivalent circuit description. The orbital relaxation dynamics continuously slows down over six decades in time, before at the lowest temperatures the glass transition becomes suppressed by quantum tunnelling.