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 separate d by graphitic matrices are fabricated by a cosputtering method. The struct ure and magnetic properties of the films are studied. An improvement in the ir magnetic properties by optimizing the alloy ratio will be demonstrated. Transmission electron microscopic (TEM) observation shows nanoparticles wit h a small mean diameter (similar to 7 nm) and narrow size distribution (sim ilar 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 m anifests a maximum value of 907 Oe at x = 0.83. The increase can be explain ed 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.