Theory of Half-metallic Ferrimagnetism in Double Perovskites

TL;DR

This paper develops a comprehensive theory for the temperature and disorder dependence of half-metallic ferrimagnetism in double perovskite Sr$_2$FeMoO$_6$, providing insights into magnetization, polarization, and ways to enhance Curie temperature.

Contribution

It introduces an effective spin Hamiltonian validated through large-scale simulations, linking magnetization and polarization to localized Fe spins, and explores disorder effects and enhancement strategies for $T_c$.

Findings

Magnetization and polarization are proportional to Fe spin magnetization.

Disorder significantly affects $T_c$ and magnetic properties.

Proposes methods to increase $T_c$ without reducing polarization.

Abstract

We present a comprehensive theory of the temperature- and disorder-dependence of half-metallic ferrimagnetism in the double perovskite Sr$_2$FeMoO$_6$ (SFMO) with $T_c$ above room temperature. We show that the magnetization $M(T)$ and conduction electron polarization $P(T)$ are both proportional to the magnetization $M_S(T)$ of localized Fe spins. We derive and validate an effective spin Hamiltonian, amenable to large-scale three-dimensional simulations. We show how $M(T)$ and $T_c$ are affected by disorder, ubiquitous in these materials. We suggest a way to enhance $T_c$ in SFMO without sacrificing polarization.