Effect of Ca Addition on Soft Magnetic Properties of Nanocrystalline Fe-Based Alloy Ribbons

The effect of Ca addition on the magnetic properties of a nanocrystalline Fe-based alloy was investigated. A small amount of Ca (0.06 wt%) was added to the Fe-based alloy, which was then melt spun to fabricate thin ribbons with a thickness of ~30 ${\mu}m$. These ribbons were heat treated to obtain a nanocrystalline structure with a grain size of ~10 nm, and the crystallization behavior was studied to optimize the grain structure. The characteristics of the ribbon alloys were analyzed using a B-H meter, a 4-point probe, a transmission electron microscope (TEM), and a scanning electron microscope (SEM). As a result, the optimum permeability and minimum core loss were obtained for the alloy containing Ca, when annealed at $520^{\circ}C$ for 1 h. The analyses revealed that a reduced core loss could be attributed to the high electrical resistivity and suppressed grain growth, which were caused by the Ca element distributed along the grain boundary. Based on the results, Ca addition to Fe-Si-B-Nb-Cu base nanocrystalline alloy was very effective in controlling the grain size, minimizing the eddy current loss, inducing an improved magnetization behavior, and reducing the core loss.