Magnetic state of pyrochlore Cd2Os2O7 emerging from strong competition of ligand distortions and longer-range crystalline anisotropy

TL;DR

This study uses quantum-chemical calculations to explore how ligand distortions and crystalline anisotropy influence the magnetic states of Cd2Os2O7, revealing a competition that determines magnetic ordering.

Contribution

It uncovers the competing effects of ligand distortions and anisotropic coordination on magnetic interactions in pyrochlore Cd2Os2O7, highlighting their impact on magnetic anisotropy and order.

Findings

Trigonal distortions lead to easy-plane anisotropy

Presence of distortions reverses zero-field splitting sign

Large easy-axis anisotropy stabilizes all-in/all-out order

Abstract

By many-body quantum-chemical calculations, we investigate the role of two structural effects - local ligand distortions and the anisotropic Cd-ion coordination - on the magnetic state of Cd2Os2O7, a spin S=3/2 pyrochlore. We find that these effects strongly compete, rendering the magnetic interactions and ordering crucially depend on these geometrical features. Without trigonal distortions a large easy-plane magnetic anisotropy develops. Their presence, however, reverses the sign of the zero-field splitting and causes a large easy-axis anisotropy (D = -6.8 meV), which in conjunction with the antiferromagnetic exchange interaction (J = 6.4 meV) stabilizes an all-in/all-out magnetic order. The competition uncovered here is a generic feature of pyrochlore magnets.