Magnetic State of Pyrochlore Cd2Os2O7 Emerging from Strong Competition of Ligand Distortions and Longer-Range Crystalline Anisotropy

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 dependent 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 similar or equal to -6.8 meV), which in conjunction with the antiferromagnetic exchange interaction (J similar or equal to 6: 4 meV) stabilizes an all-in-all-out magnetic order. The competition uncovered here is a generic feature of pyrochlore magnets. DOI: 10.1103/PhysRevLett.110.127206