Spin moment over 10-300 K and delocalization of magnetic electrons above the Verwey transition in magnetite

TL;DR

This study investigates the magnetic properties of magnetite across 10-300K, revealing non-integral magnetic moments, anisotropy changes, and electron delocalization above the Verwey transition through experiments and first-principles calculations.

Contribution

It provides new insights into the temperature-dependent magnetic behavior and electron delocalization in magnetite, linking spin-orbit coupling and structural frustration to the Verwey transition.

Findings

Magnetic moment $$ is non-integral and varies with magnetic field direction.

Magnetic electrons become delocalized on Fe B-sites above the Verwey temperature.

Anisotropy of magnetic profiles increases with temperature, indicating changes in electron localization.

Abstract

In order to probe the magnetic ground state, we have carried out temperature dependent magnetic Compton scattering experiments on an oriented single crystal of magnetite (Fe$_3$O$_4$), together with the corresponding first-principles band theory computations to gain insight into the measurements. An accurate value of the magnetic moment $\mu_S$ associated with unpaired spins is obtained directly over the temperature range of 10-300K. $\mu_S$ is found to be non-integral and to display an anomalous behavior with the direction of the external magnetic field near the Verwey transition. These results reveal how the magnetic properties enter the Verwey energy scale via spin-orbit coupling and the geometrical frustration of the spinel structure, even though the Curie temperature of magnetite is in excess of 800 K. The anisotropy of the magnetic Compton profiles increases through the Verwey temperature $T_v$ and indicates that magnetic electrons in the ground state of magnetite become delocalized on Fe B-sites above $T_v$.