Intergranular coupling and activation volume of Co-Ni ferrite thin films with high coercivity above 3 kOe

Co-Ni ferrite film media with high coercivity above 3 kOe were fabricated by ferrite plating and intergranular coupling and medium noise were discussed. Increase of Co content in Co-Ni ferrite thin film with a thickness of 40 mn led to a decrease of intergranular exchange coupling and activation volume, resulting in the reduction of media noise in the high frequency region. The coercivity H_c increased with the Co content, and reached 3.6 kOe. At the maximum Co content, the activation volume took the minimum value of 6.7×10 ^-18 cm³, being smaller than the volume of a single grain in the film. The medium noise was kept almost constant up to the linear recording density of 144 kfrpi, while the noise of the media with the lower Co content and lower H_c increased with the linear recording density