Interactions between structural and magnetic domains through the Verwey transition in stoichiometric and doped magnetite

The magnetic response of magnetite as it cycles through the Verwey transition at $T_{\rm V}\approx 120$ K remains incompletely understood, despite numerous studies of both structural and magnetic domains. For example, although the alternating-current susceptibility increases upon heating through the Verwey temperature $T_{\rm V}$, the magnetization may either increase or decrease. Since many intertwined processes occur at $T_{\rm V}$, a multifaceted view of the magnetic changes may help clarify the nature of these processes and establish specific features of the transition as diagnostic tools. To this end, we report measurements of the magnetic response of magnetite upon heating through $T_{\rm V}$ under a wide range of applied-field conditions. We studied synthetic stoichiometric and doped (Zn, Ti, and Al) single crystals, as well as a natural polycrystalline sample, with the aim of explaining how and why the magnetization changes as a function of temperature through $T_{\rm V}$. The magnetic-field-induced reorientation of the monoclinic $c$ axis may broaden the transition, primarily in stoichiometric magnetite. These findings help clarify the mechanism of the transition.