Superparamagnetic behavior of structural domains in epitaxial ultrathin magnetite films

Abstract

We provide evidence that thin films of magnetite ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ epitaxially grown on single-crystalline MgO(100), form domains with unique magnetic properties. Strong 180\ifmmode^\circ\else\textdegree\fi{} Fe-O-Fe superexchange paths at antiphase domain boundaries result in a frustration of the interdomain interactions. Probe-layer M\"ossbauer spectroscopy shows superparamagnetic behavior in the entire film, in spite of the nearly perfect layer-by-layer growth. Superconducting quantum interference device magnetometry is used to determine the temperature and thickness dependence of the superparamagnetic blocking temperatures.