Desirable Measurement on Accurate Hysteresis Curve for Large Nd–Fe–B Sintered Magnets at Elevated Temperatures

Abstract

To obtain an accurate hysteresis curve in large Nd–Fe–B sintered magnets at elevated temperatures, we compared the hysteresis curves obtained from the following methods: a superconducting magnet-based vibrating sample magnetometer (SCM-VSM) and the hysteresis graph (HG). Attention was paid to the values of $dJ/dH$ near $H_{\mathrm {cJ}}$ and $H_{k}/H_{\mathrm {cJ}}$ , where $J$ , $H$ , $H_{\mathrm {cJ}}$ , and $H_{k}$ are the magnetization, the magnetic field, coercivity, and knee field, respectively. In the HG method, greater dimensional ratio ( $L/D$ ) led to easier uniform magnetization of cylindrical magnets, causing larger $L/D$ to improve $dJ/dH$ near $H_{\mathrm {cJ}}$ and $H_{k}/H_{\mathrm {cJ}}$ . However, the magnetization distortion did not appear at all in the SCM-VSM method at various temperatures and, thus, we could measure the values of $dJ/dH$ near $H_{\mathrm {cJ}}$ and $H_{k}/H_{\mathrm {cJ}}$ as well as the hysteresis curve exactly.