Magnetic properties of Co-Ni-Fe-N nanocrystalline thin films

Co-Ni-Fe-N soft magnetic thin films were fabricated by a N₂ reactive RF magnetron sputtering method. The nitrogen partial pressure (P_N2) was varied in the range of 0-10%. As P_N2 increases in this range, the saturation magnetization B_s linearly decreases from 19.8 to 14 kGs and the electrical resistivity ρ increases from 27 to 155 μΩ cm. The coercivity H_c exhibits the minimum value at 4% P_N2. The magnetic anisotropy field H_k is in the range of 20-40 Oe. High frequency characteristics of (Co_22.2Ni_27.6Fe_50.2)_100-xN _x films are excellent in the range of 3%-5% P_N2. Especially, the effective permeability μ_eff of the film fabricated at 4% P_N2 is about 800, which is maintained up to 600 MHz. The corrosion resistance of these films is improved with increase of N concentration. Moreover, the thickness effects on the high frequency characteristics of these films were investigated in the range of 0.01-1.0 μm. It is found that B_s of these films decreases with decrease in film thickness below 0.5 μm, which is due to decrease in Fe content in the film composition, whereas H_c increase largely with the decrease in film thickness. The electrical resistivity ρ also increases with the decrease in film thickness, especially below 0.1 μm, but μ_eff of Co-Ni-Fe-N thin films maintained up to above 700 MHz below 0.3 μm in thickness. From XRD, TEM and FMR results, these films are formed in an amorphous phase during the initial growth stage and it gradually changes to crystalline structure as the film thickness increases.