High-Frequency Magnetic Properties of Nd2Fe17N3 Magnetic Powders with Nano-α-Fe Phase-Separated Surface Layers

In this study, Nd2Fe17N3 powders were coated with transition metals and rare-earth phosphate layers. The phosphate layers were subsequently phase-separated into outer Fe2O3 and inner Nd2O3 layers via heat treatment in air. Simultaneously, phase-separated layers of nano-sized α-Fe and rare-earth rich phases were formed in the interface between the Nd2Fe17N3 and phosphate layer. The resulting powder was classified into particle sizes of 20–38 µm, formed into a toroidal core shape, and then measured for magnetic properties in the MHz range. The real permeability µ′ and loss tangent tanδ values at 10 MHz were approximately 11.19 and 0.02, respectively. The treated powder exhibited a two-fold enhancement and 10-fold reduction in the values of µ′ and tanδ, respectively, compared to those of the untreated Nd2Fe17N3 powder. The developed treatment protocols enable the synthesis of magnetic powders that possess both magnetic coupling and insulating properties, which will facilitate the development of MHz-range magnetic cores.

I. Introduction

In recent years, the development of high-frequency switching devices using materials like GaN and SiC has drawn attention to fulfill the need for power circuits with higher frequencies, which require smaller, lighter, and more compact circuits. However, the development of passive elements paired with switching devices, particularly magnetic materials used as core materials for transformers and noise filters, has not received significant attention. Mn-Zn ferrite cores, which are currently the conventional core material for transformers, have the disadvantage of reaching the Snoke’s limit at several MHz, resulting in a decrease in magnetic permeability.