Magnetic properties of hematite revealed by an ab initio parameterized spin model

TL;DR

This study combines ab initio calculations and spin dynamics simulations to elucidate hematite's magnetic properties, accurately predicting phase transitions and magnetic behaviors relevant for spintronics applications.

Contribution

It introduces a parameterized spin model based on ab initio data to analyze hematite's magnetic properties and phase transitions.

Findings

Computed Ne9el temperature and canting angle match experiments

Revealed the role of dipole interactions and anisotropies in magnetic phases

Identified deviations at low temperatures due to quantum fluctuations

Abstract

Hematite is a canted antiferromagnetic insulator, promising for applications in spintronics. Here, we present ab initio calculations of the tensorial exchange interactions of hematite and use them to understand its magnetic properties by parameterizing a semiclassical Heisenberg spin model. Using atomistic spin dynamics simulations, we calculate the equilibrium properties and phase transitions of hematite, most notably the Morin transition. The computed isotropic and Dzyaloshinskii--Moriya interactions result in a N\'eel temperature and weak ferromagnetic canting angle that are in good agreement with experimental measurements. Our simulations show how dipole-dipole interactions act in a delicate balance with first and higher-order on-site anisotropies to determine the material's magnetic phase. Comparison with spin-Hall magnetoresistance measurements on a hematite single-crystal reveals deviations of the critical behavior at low temperatures. Based on a mean-field model, we argue that these differences result from the quantum nature of the fluctuations that drive the phase transitions.