Magnetite and the Verwey transition, from γ-rays to low-energy electrons

Abstract

Magnetite, a semiconducting ferrimagnetic iron spinel with a metal-insulator phase transition, the Verwey transition, has long been the subject of Mossbauer spectroscopy studies, which continue today. We review the current status of the understanding of the Mossbauer spectra of magnetite. Furthermore, magnetite is a very attractive material in current topics such as spintronics. In this particular subject, to determine the behavior of magnetic domains is paramount, and the changes ocurring on the near surface region upon undergoing the Verwey transition are relevant. In order to advance in this area, we have incorporated some new techniques, namely microscopy observations made with low-energy electrons. These observations can be performed upon changing the temperature, and can provide magnetic contrast through the use of spin-polarized electrons. By this means, we have observed the ferroelastic transformation associated with the Verwey transition, discovered an order-disorder transition of the (001) surface of magnetite and observed the changes in the magnetic domains on the same surface by changing the temperature. Low-energy electrons also are the key to the Mossbauer experiments of magnetite films and surfaces, with the promise of providing surface-sensitive spatially resolved Mossbauer spectra.