Effects of post-annealing on the magnetic properties of FeCoBN thin films

In this work, the effects of the applied magnetic field and post-annealing on the magnetic properties of Fe₇Co₃BN thin films are studied. Annealing is conducted at 200°C with application of a uniform magnetic field of ∼4 kOe parallel to the direction of easy magnetization. Results show that the magnetization curves in the as-deposited films clearly show the existence of stripe domains. Formation of the stripe domains deteriorates the high frequency characteristics of the films. On contrary, the post-annealing effectively linearizes the magnetization curves, which results in the sharp decrease of coercivity H_c. In addition, magnetic anisotropy H_k of the annealed films is increased with B contents and H_k of the film deposited reaches 110 Oe, indicating ferromagnetic resonance frequency f_FMR of 4 GHz. The grain size of the films are found to be around 10 nm, which show not any noticeable change of grain size by post-annealing. Also, X-ray diffraction patterns show that the residual stress is relieved. This clearly indicate that post-annealing may effectively release the residual stress without any microstructural changes. The removal of the residual stress is shown to improve the high frequency characteristics of the annealed films.