Magnetisation reversal of epitaxial films of γ'-Fe4N on Cu(100)

Epitaxial single-phase gamma'-Fe4N(100) thin films have been grown on Cu(100). The growth mode and structure have been studied from the early stages up to 50nm thick films by means of in situ scanning tunnelling microscopy, low-energy electron diffraction and Auger electron spectroscopy. The nitride films are single crystals with sharp interfaces with the substrate, atomically flat and grown layer by layer. The magnetic properties have been studied ex situ by high-resolution vectorial Kerr magnetometry. The films are ferromagnetic at room temperature. The magnetisation lies within the plane of the film. The hysteresis loops are non-consistent with a simple cubic symmetry. Two easy axes, close to the 100 directions, but at 81 deg from each other, are found. The angular dependence of the vector hysteresis loops reveals different magnetisation reversal behaviours around the two hard-axes directions and around the two easy-axes directions. The origin of these features is discussed.