Regensburg 2013 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 41: Focussed Session: Frontiers of Electronic Structure Theory IV (jointly with HL and TT)
O 41.11: Vortrag
Mittwoch, 13. März 2013, 13:15–13:30, H36
Magnetic state of pyrochlore Cd2Os2O7 emerging from strong competition of ligand distortions and longer-range crystal anisotropy — •Nikolay Bogdanov1, Remi Maurice2, Ioannis Rousochatzakis1, Jeroen van den Brink1, and Liviu Hozoi1 — 1IFW Dresden, Germany — 2Groningen University, The Netherlands
We investigate the correlated d-level electronic structure of Cd2Os2O7, a spin S=3/2 pyrochlore, by fully ab initio quantum-chemical many-body calculations on finite embedded clusters. The wave-function quantum-chemical methods provide a promising alternative to density-functional-based approaches to the electronic structure of solids. We describe the local Os d3 multiplet structure, the precise mechanism of second-order spin-orbit coupling and zero-field splitting (ZFS), and determine the parameters of the effective spin Hamiltonian, i.e., the single-ion anisotropy, nearest-neighbor Heisenberg exchange as well as the Dzyaloshinskii-Moriya interactions.
The results indicate that local ligand distortions and the anisotropic Cd-ion coordination 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 ZFS 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 227 pyrochlore magnets and opens new perspectives on the basic magnetism in these materials.