Effects of utilizing a granular nucleation layer on magnetic properties and microstructure of CoPt–B₂O₃ granular medium

The magnetic properties and microstructure of Co₈₀Pt₂₀–30 vol % B₂O₃ granular medium deposited on nucleation layers (NLs) with Co₈₀Pt₂₀–30 vol % oxides (oxides: Nb₂O₅, WO₃, Ta₂O₅, SiO₂, TiO₂, Al₂O₃, Cr₂O₃, and ZrO₂) of various thicknesses were investigated. By introducing an NL, a granular medium with columnar growth of small magnetic grains can be obtained. Furthermore, magnetic grains are separated with an oxide grain boundary material from the initial growth region that promotes the decoupling of magnetic grains, which corresponds to an increase in coercivity. The degrees of diameter reduction and decoupling of magnetic grains depend on the NL thickness and the melting point of the oxide utilized in the NL.