Improvements of irreversible thermal losses in anisotropic Nd2Fe14B-based resin-bonded permanent magnets made from HDDR powder

Abstract

The relationship between the intrinsic coercivity (HcJ) and irreversible magnetic flux losses at elevated temperatures has been studied on compression-molded, resin-bonded anisotropic magnets made from Nd2Fe14B-type hard magnetic powders prepared by means of the hydrogenation–disproportionation–desorption–recombination (HDDR) process. Powders with various HcJ values were prepared by partial substitution of Dy for Nd, and the temperature dependence of HcJ of these powders were investigated. The HcJ values range from 0.86 to 1.3 MAm−1 at room temperature. A rule of thumb has been found that the minimum room temperature value of HcJ required to reduce the irreversible losses to the level comparable to the values encountered in rapidly-solidified, isotropic Nd2Fe14B (HcJ=0.76 MAm−1) magnets is 1.2 MAm−1. The difference in the HcJ values to yield similar losses in these two types of materials is attributed to the difference in the temperature dependence of HcJ. The dependence of the magnetizability on temperature of these magnets has also been studied. It is demonstrated that moderate heating of the magnets significantly increases the magnetic flux density obtainable below the magnetizing temperature when the magnetizing force is not large enough to saturate the magnet. In such cases, frequently encountered in actual applications, the magnetic flux density is stabilized in the temperature range below the magnetizing temperature.