Perpendicular Anisotropy of Iron Nitride Thin Films Prepared by Ion-Assisted Vapor Deposition

Iron nitride thin films with perpendicular magnetic anisotropy were prepared by ion-assisted vapor deposition. The films exhibited a large perpendicular magnetic anisotropy field (above 2.5 kOe). A columnar structure was found to grow normal to the substrate. The films consisted of paramagnetic ¿-Fe2N and ¿-Fe2-3N phases and ferromagnetic ¿-Fe and ¿´-Fe4N phases. The perpendicular anisotropy may be attributed mainly to the shape anisotropy of the perpendicularly oriented columnar structure and to the magnetic separation effect due to segregation of paramagnetic components along each column. It was also found that a large perpendicular anisotropy is obtained more easily by irradiation with a nitrogen ion beam at low angles such as 10° to 30° from the substrate, rather than at large angles such as 70°.