Coupled spin-lattice fluctuations in a compound with orbital degrees of freedom: the Cr based dimer system Sr3Cr2O8

TL;DR

This study investigates the complex spin, lattice, and orbital fluctuations in Sr3Cr2O8, revealing multiple transition temperatures, phonon anomalies, and excitation gaps through Raman scattering and magnetic measurements.

Contribution

It uncovers the interplay of spin, lattice, and orbital degrees of freedom in Sr3Cr2O8, highlighting distinct fluctuation regimes and excitation gaps not previously characterized.

Findings

Anomalies in Raman-active phonons and magnetic scattering indicate fluctuation regimes.

Identification of a spin excitation gap from two- and three-magnon scattering.

Observation of exponential phonon linewidth decrease below T*.

Abstract

We report on an extended fluctuation regime in the spin dimer system Sr3Cr2O8 based on anomalies in Raman active phonons and magnetic scattering. The compound has two characteristic temperatures, TS = 275 K, related to a Jahn-Teller transition with structural distortions and orbital ordering and a second, T*= 150 K, which is due to further changes in the orbital sector. Below TS quasielastic scattering marks strong fluctuations and in addition phonon anomalies are observed. For temperatures below T* we observe an exponential decrease of one phonon linewidth and determine a gap of the orbital excitations. At low temperatures the observation of two- and three-magnon scattering allows the determination of the spin excitation gap.