Conversion electron Mِssbauer spectroscopy studies of ultrathin Fe films on MgO(0 0 1)

The initial growth and influence of annealing on structural and magnetic properties of 5 monolayers epitaxial Fe films on cleaved and polished MgO(0 0 1) substrates was studied using conversion electron Mössbauer spectroscopy (CEMS). Broadening of LEED spots indicated a granular structure of the films grown at room temperature. The CEMS analysis showed that the film on the cleaved substrate is flat and consists of a 2 ML interfacial layer with the electronic structure affected by the oxidic substrate, while the remaining 3 ML are metallic with the Curie temperature below RT. Annealing changes the film structure, as seen by CEMS, but only for temperatures above 550 K. In the annealing process the continuous film breaks into 3-dimensional islands and oxidation takes place at the Fe/cleaved–MgO interface. On the polished substrate, the as-prepared film consists of small superparamagnetic metallic iron particles. Contrary to the cleaved substrate, no oxidation is observed at the interface upon annealing.