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.