Abnormal temperature dependence of intrinsic coercivity in sintered Sm–Co-based permanent magnets

Abstract

In search of high-temperature permanent magnet materials, sintered Sm–Co-based magnets with abnormal temperature dependence of intrinsic coercivity have been obtained. These magnets have small negative, or near-zero, or large positive temperature coefficients of intrinsic coercivity. A model of coercivity mechanism has been proposed to explain this abnormal temperature dependence. According to this model, the coercivity in 2:17-type permanent magnets is controlled by two conflicting mechanisms. The first mechanism is thermal activation, which leads to decreased coercivity with increasing temperature. The second mechanism can be explained by a pinning process in which increasing temperature may result in an increased difference of crystalline anisotropy between the 2:17 cell phase and 1:5 cell boundary phase and, in turn, a higher coercivity at high temperature.