Roles of cobalt and boron in FeCoBSi soft magnetic composite with in-plane uniaxial magnetic anisotropy

The roles of cobalt and boron in an FeCoBSi soft magnetic composite (SMC) containing magnetic flakes with in-plane uniaxial magnetic anisotropy were investigated. When cobalt was added to the magnetic flakes in the SMC, in-plane uniaxial magnetic anisotropy was effectively induced, and coercivity in the easy axis direction remarkably decreased after annealing under a magnetic field in comparison with the case without addition of cobalt. In particular, the addition of cobalt was essential to decrease coercivity in the SMC, in marked contrast to simple amorphous ribbons in which coercivity decreased even without addition of cobalt but in-plane uniaxial magnetic anisotropy was not induced. Boron prevented crystallization of the magnetic amorphous phase, with boron content of more than approximately 18 at% relative to FeCo necessary to produce an amorphous phase without crystallization, resulting in low coercivity and in-plane uniaxial magnetic anisotropy. High saturation magnetization of 1.12 T and low coercivity of 0.32 Oe with in-plane uniaxial magnetic anisotropy were obtained with a composition of Fe_55.5Co_23.7B_14.2Si_6.6 (Co/(Fe + Co) = 30 at% and B/(Fe + Co) = 18 at%) in the fabricated SMC.