Ferrimagnetic/ferroelastic domain interactions in magnetite below the Verwey transition: Part II. Micromagnetic and image simulations

Abstract

Micromagnetic simulations have been used to explore the interaction between ferrimagnetic domain walls (DWs) and ferroelastic twin walls (TWs) below the Verwey transition in magnetite (Fe₃O₄). Simulations were performed using a thin-foil geometry in order to replicate the domain patterns observed experimentally using transmission electron microscopy. The magnetic microstructure is shown to be highly sensitive to the physical dimensions and crystallographic orientation of the foil, the spatial distribution and crystallographic classification of the TWs and the temperature/field history of the sample. A method to calculate the phase shift of a beam of electrons passing through the micromagnetic simulations is applied. The resulting phase maps provide a robust interpretation of experimental images obtained using Fresnel-mode Lorentz microscopy and off-axis electron holography. The interaction between ferrimagnetic and ferroelastic DWs during field cycling provides an explanation for the low-temperature ‘field-memory effect’ in magnetite.

Keywords:

• magnetite
• Verwey transition
• twins
• domain walls
• micromagnetics
• electron holography
• Lorentz microscopy

Acknowledgements

The authors thank M. Scheinfein for providing the custom LLG micromagnetic software and M. Beleggia for useful discussions. Financial support from NERC is also acknowledged.