Ferromagnetic Exchange Anisotropy from Antiferromagnetic Superexchange in the Mixed 3d-5d Transition-Metal Compound Sr3CuIrO6

TL;DR

This study uncovers a novel ferromagnetic exchange anisotropy mechanism in Sr3CuIrO6, driven by antiferromagnetic superexchange influenced by spin-orbit coupling differences, revealing unique magnetic behaviors in mixed 3d-5d transition-metal compounds.

Contribution

It demonstrates a new exchange anisotropy mechanism caused by spin-orbit coupling effects in a mixed 3d-5d transition-metal compound, supported by experimental and theoretical analysis.

Findings

Large gap magnetic excitation spectrum observed.

Unusual ferromagnetic anisotropy from antiferromagnetic superexchange.

Mechanism likely present in similar edge-sharing transition-metal systems.

Abstract

We report a combined experimental and theoretical study of the unusual ferromagnetism in the one-dimensional copper-iridium oxide Sr$_3$CuIrO$_6$. Utilizing Ir $L_3$ edge resonant inelastic x-ray scattering, we reveal a large gap magnetic excitation spectrum. We find that it is caused by an unusual exchange anisotropy generating mechanism, namely, strong ferromagnetic anisotropy arising from antiferromagnetic superexchange, driven by the alternating strong and weak spin-orbit coupling on the $5d$ Ir and 3d Cu magnetic ions, respectively. From symmetry consideration, this novel mechanism is generally present in systems with edge-sharing Cu$^{2+}$O$_4$ plaquettes and Ir$^{4+}$O$_6$ octahedra. Our results point to unusual magnetic behavior to be expected in mixed 3d-5d transition-metal compounds via exchange pathways that are absent in pure 3d or 5d compounds.