Spin-phonon coupling in antiferromagnetic chromium spinels

TL;DR

This study investigates how spin-phonon coupling affects phonon modes in various antiferromagnetic chromium spinels across temperatures, revealing mode splittings linked to magnetic order and frustration.

Contribution

It provides detailed IR spectroscopy analysis of spin-phonon interactions in multiple chromium spinels, highlighting the influence of magnetic frustration and order on phonon behavior.

Findings

Significant phonon mode splittings occur at magnetic transitions.

Splitting patterns vary with the type of magnetic frustration.

HgCr2S4 shows no splitting but exhibits shifts due to ferromagnetic fluctuations.

Abstract

The temperature dependence of eigenfrequencies and intensities of the IR active modes has been investigated for the antiferromagnetic chromium spinel compounds CdCr2O4, ZnCr2O4, ZnCr2S4, ZnCr2Se4, and HgCr2S4 by IR spectroscopy for temperatures from 5 K to 300 K. At the transition into the magnetically ordered phases, and driven by spin-phonon coupling, most compounds reveal significant splittings of the phonon modes. This is true for geometrically frustrated CdCr2O4, and ZnCr2O4, for bond frustrated ZnCr2S4 and for ZnCr2Se4, which also is bond frustrated, but dominated by ferromagnetic exchange. The pattern of splitting is different for the different compounds and crucially depends on the nature of frustration and of the resulting spin order. HgCr2S4, which is almost ferromagnetic, exhibits no splitting of the eigenfrequencies, but shows significant shifts due to ferromagnetic spin fluctuations.