Abstract
Double perovskite is (or is very close to) a realization of a spin-asymmetric semimetallic compensated ferrimagnet, according to first principles calculations. This type of near-half metallic antiferromagnet is an unusual occurrence, and more so in this compound because the zero gap is accidental rather than being symmetry determined. The large spin-orbit coupling (SOC) of osmium upsets the spin balance (no net spin moment without SOC): it reduces the Os spin moment by and induces an Os orbital moment of in the opposite directions. The effects combine (with small oxygen contributions) to give a net total moment of per cell in , reflecting a large impact of SOC in this compound. This value is in moderately good agreement with the measured saturation moment of . The value of the net moment on the Os ion obtained from neutron diffraction ( at low temperature) differs from the calculated value . Rather surprisingly, in isovalent , the smaller SOC-induced spin changes and orbital moments (mostly on Ru) almost exactly cancel. This makes a “half (semi)metallic antiferromagnet” (practically vanishing net total moment) even when SOC is included, with the metallic channel being a small-band-overlap semimetal. Fixed spin moment (FSM) calculations are presented for each compound, illustrating how they provide different information than in the case of a nonmagnetic material. These FSM results indicate that the Cr moment is an order of magnitude stiffer against longitudinal fluctuations than is the Os moment.
- Received 29 August 2007
DOI:https://doi.org/10.1103/PhysRevB.77.115101
©2008 American Physical Society