SEMINAR: Physics Seminar

Magnetic thin films with their magnetic moments spontaneously aligned perpendicular to the film plane are of great interest for their practical applications. This configuration is applied in perpendicular recording media with increased data storage density. New materials with a larger tendency to align perpendicular to the plane (i.e. with larger perpendicular anisotropy) could further increase the storage density.

One way to induce perpendicular anisotropy is by distorting the lattice of single crystalline films. In cubic lattices the distortion along the c axis lowers the symmetry causing an increased orbital moment and the spin-orbit coupling forces the moment to align perpendicular to the film plane. A large perpendicular anisotropy in tetragonally distorted Fe100-xCox alloys was theoretically predicted for bulk materials [1]. Experimentally this was achieved by growing thin films on substrates with mismatched lattice parameters such as Rh and Ir(001) [2]. The interface between the substrate and the film can significantly influence the magnetic behaviour but was not considered in the theoretical prediction. Furthermore the distortion can be expected to relax as the film is made thicker and approaches bulk-like behaviour but the mechanism of this relaxation remains unclear.

The Fe100-xCox /Ir(001) system has been studied in an attempt to understand the correlation between film structure, nature of the interface and structural relaxation to the magnetic properties. An onset of ferromagnetic ordering and the increase and decay of the perpendicular anisotropy with the composition and thickness were observed. Comparison between the magnetic behaviour of Fe100-xCox on Ir and Rh(001) surfaces highlight the peculiar properties of the Ir(001) surface and may shed light on the mechanism for inducing perpendicular anisotropy by tetragonal distortion.

[1] T. Burkert et al., Phys. Rev. Lett. 93, 027203 (2004). [2] F. Yildiz et al., J. Appl. Phys. 105, 07E129 (2009).