Magnetic Properties of Pure Iron Soft Magnetic Composites Coated by Manganese Phosphates

Soft magnetic composites using metallic magnetic powders have extensively been investigated for the application to mobile electromagnetic devices, particularly motor cores. These metal powders are strongly required to be insulated from one another for low eddy-current losses. In addition, the insulation layer of the powders should possess high thermal stability for low hysteresis losses. Despite poor thermal stability, the iron phosphate coating on iron powders is still widely used because of a well-established technology. In this paper, we focused on the development of manganese phosphate coating on iron powders to overcome the low thermal stability of iron phosphate. It was shown that manganese phosphate insulation layers were thermally stable up to 600 °C. The core loss of composites with manganese phosphate-coated powders annealed at 600 °C measured 35.67 W/kg and the eddy-current loss 5.65 W/kg, indicating that excellent insulation coating layers were formed.