Changes in Magnetic Properties and Structure of Nitrogen Added Fe-Co Multilayered Films by Annealing

Fe/Co multilayer films with nitrogen added were annealed in a vacuum with a 500 Oe rotating magnetic field. Annealing at an appropriate temperature causes decomposition of nitride phases such as Fe4, Co4 and (FeCo)4N though the temperature at which such decomposition occurs increases from 200°C to 350°C as the layer period dlayer is increased from 36 Å to 470 Å. The film accordingly loses its layered structure and becomes a uniform Fe-Co alloy film. Changes in the magnetization curve of films with the annealing temperature indicate that film with low coercivity is composed of Fe-N and Co-N layers with a small magnetic anisotropy and of Fe-Co-N layers with a large uniaxial magnetic anisotropy. Changes in the coercive force Hc with the annealing temperature depend on the compositional modulation wavelength dlayer, though all films with dlayer larger than 60 Å have nearly the same minimum Hc value of about 1 Oe.