Ni1-xCox-C nanogranular thin films prepared by a co-sputtering method:: Improvement in magnetic properties by optimizing the alloy ratio

Nanogranular thin films consisting of Ni1-xCox alloy nanoparticles separated by graphitic matrices are fabricated by a cosputtering method. The structure and magnetic properties of the films are studied. An improvement in their magnetic properties by optimizing the alloy ratio will be demonstrated. Transmission electron microscopic (TEM) observation shows nanoparticles with a small mean diameter (similar to 7 nm) and narrow size distribution (similar to 20% of mean diameter) at the Co/(Ni + Co) ratio (x) ranging from 0 to 0.83. In this region, the coercivity continuously increases with x and manifests a maximum value of 907 Oe at x = 0.83. The increase can be explained in terms of alloy formation. With further increasing x up to x = 1, the coercivity decreases. The decrease is caused by the existence of extremely large Co particles, which are revealed by TEM observation.