High-Frequency Magnetic Properties of Novel Sm–Mo–Fe Phosphate-Coated Fe–X (X = Ni and Mn) Magnetic Powder Cores

In this study, we developed a new magnetic powder core using Fe– $X$ powders, which has a coercivity of less than 80 A/m and a saturation magnetization comparable to that of pure iron powders. Fe– $X$ powders doped with 4 at% nickel and 0.1 at% manganese were fabricated by the reduction of Ni–Mn doped ferrite (Fe0.959Ni0.04Mn0.001)3O4 nanopowders with hydrogen gas at 1323 K. The magnetic powder cores were prepared from Fe– $X$ powders coated with the novel phosphate insulators developed using rare earth and transition metals. The as-produced insulator was more thermally stable than conventional phosphate insulators and maintained its properties even after annealing at 873 K. After annealing, the Sm–Mo–Fe phosphate insulating layer separated into a samarium-rich and transition-metal-rich layer. The magnetic powder core of Fe– $X$ ( $X$ = Ni and Mn) powders coated with the Sm–Mo–Fe phosphate insulator, compacted at 1.47 GPa with heat treatment at 793 K, having a density of 7.62 Mg/m3, and exhibited magnetic flux density at 10 kA/m of 1.66 T. Iron loss $W_{10/400}$ ( $B_{\text {max}}$ = 1 T, $f$ = 400 Hz) was 38 W/kg and $W_{0.5/20\,\text {k}}$ ( $B_{\text {max}}$ = 0.05 T, $f$ = 20 kHz) was 43 W/kg.