Double perovskites like Sr2FeMoO6 are materials with half-metallic ground states and ferrimagnetic Tc's well above room temperature. This paper is the second of our comprehensive theory for half metallic double perovskites. Here we derive an effective Hamiltonian for the Fe core spins by "integrating out" the itinerant Mo electrons and obtain an unusual double square-root form of the spin-spin interaction. We validate the classical spin Hamiltonian by comparing its results with those of the full quantum treatment presented in the companion paper "Theory of Half-Metallic Double Perovskites I: Double Exchange Mechanism". We then use the effective Hamiltonian to compute magnetic properties as a function of temperature and disorder and discuss the effect of excess Mo, excess Fe, and anti-site disorder on the magnetization and Tc. We conclude with a proposal to increase Tc without sacrificing carrier polarization.
@article{arxiv.1210.6689,
title = {Theory of Half-Metallic Double Perovskites II: Effective Spin Hamiltonian and Disorder Effects},
author = {Onur Erten and O. Nganba Meetei and Anamitra Mukherjee and Mohit Randeria and Nandini Trivedi and Patrick Woodward},
journal= {arXiv preprint arXiv:1210.6689},
year = {2013}
}