Microstructure of Nd2Fe17N3 Magnetic Powder Surface with Nano-α-Fe Phases Separated Surface Layer

We investigated the application of Nd2Fe17N3 magnetic powder with planar magnetic anisotropy to magnetic field amplification materials at several tens of MHz. Consequently, we succeeded in developing a magnetic property with µ′ ~ 8 and at 10 MHz using a phosphoric acid coating and a simple heat treatment process in air. In this study, microstructural analysis by transmission electron microscopy and X-ray diffraction revealed that the coating layer became thicker and the Nd2Fe17N3 surface was phase-separated into nano-sized α-Fe phases and Nd-rich phases, either oxide, oxynitride, or nitride. Additionally, the nano-sized α-Fe phases and the nano-sized Nd-rich phases were oriented over a wide area spanning several hundred nanometers. We concluded that these characteristic structures have led to improved properties.

I. Introduction

Re₂Fe₁₇N₃ magnetic materials have been extensively studied. Sm₂Fe₁₇N₃ was developed by Coey et al. [1] and Iriyama et al. [2]. It is widely used as a bond magnet because of its uniaxial magnetic anisotropy, high saturation magnetization, and high magnetic anisotropy. However, when rare earth elements such as Nd and Ce are used, they exhibit planar magnetic anisotropy; thus, few studies have been conducted for practical applications. However, recently, applications in the MHz to GHz bands have begun to be considered. Imaoka et al. [3] [4] and a group of researchers at Lanzhou University [5] conducted a study on electromagnetic wave-absorbing materials in the GHz band. Ide et al. [6] investigated the application of Nd₂Fe₁₇N₃ materials to the magnetic core of a series resonance circuit for GaN wireless power transmission.