Effects of Co addition on microstructure and magnetic properties of ferromagnetic CoFeSiB alloy films

A correlation between composition, microstructure, and magnetic properties of sputter-deposited CoFeSiB alloy films has been studied. Various analytical tools and micromagnetic models were employed to understand the details of microstructural evolution and magnetic reversal processes, respectively. The CoFeSiB alloy film shows significantly different microstructure and magnetic properties depend on the Co concentration. When the Co concentration is below 75 at.%, the alloy has an amorphous phase exhibiting magnetic softness with negative remanence. Meanwhile, beyond 75 at.%, the structure consists of nanocrystals precipitated in the amorphous matrix, which becomes magnetically hard with positive remanence as well as antiferromagnetic exchange coupling.