Strong magneto-optical effects in ACr2O4 A=Fe, Co spinel oxides generated by tetrahedrally coordinated transition metal ions

TL;DR

This study demonstrates significant magneto-optical Kerr effects in ACr2O4 spinel oxides with non-collinear spin orders, highlighting the role of tetrahedrally coordinated transition metal ions in enhancing optical responses.

Contribution

It reveals large magneto-optical Kerr rotation in ACr2O4 spinels, especially unprecedentedly high in CoCr2O4, due to on-site d-d transitions of tetrahedrally coordinated Co2+ ions.

Findings

Large Kerr rotation observed at A2+ ion transitions

Unprecedented 12° Kerr rotation in CoCr2O4

Strong magneto-optical effects linked to tetrahedral Co2+ ions

Abstract

Magneto-optical effects have been investigated over the infrared{visible spectral range in ACr2O4 (A = Fe, Co) spinel oxides with non-collinear spin orders in their ground states. We found large magneto-optical Kerr rotation and ellipticity at the on-site d-d transitions of the A2+ ions located within the charge gap. The magneto-optical Kerr rotation of 12 deg observed in CoCr2O4 is unprecedentedly large among magnetic semiconductors and points towards the uniqueness of tetrahedrally coordinated Co2+ ions in generating a strong magneto-optical response. Criteria of strong magneto-optical effects emerging at on-site d-d transitions of transition metal ions are discussed.