Optimizing temperature coefficient of Sm2Co17-type magnets through adjusting the isothermal aging process

The high-temperature magnetic performance and microstructure of Sm_1–xGd_x(Co_balFe_0.09Cu_0.09Zr_0.025)_7.2 (x = 0.3, 0.5) magnets were investigated. With the isothermal aging time decreasing from 11 to 3 h, the temperature coefficient of intrinsic coercivity in the temperature range of 25–500 °C, β_{25–500 °C}, was optimized from −0.167%/°C to −0.112%/°C for x = 0.3 magnets. The noticeable enhancement (∼33%) of temperature stability is correlated with the increased content of 1:5H cell boundary phase and its relatively high Curie temperature as well. However, for the x = 0.5 magnet, it is found that the presence of Sm₅Co₁₉ phases and wider nanotwin variants hinder the formation of 1:5H cell boundary phase. The insufficient 1:5H is not beneficial to the proper redistribution of Cu in cell boundary, making the x = 0.5 magnet difficult to achieve higher temperature stability. Consequently, the approach of adjusting the isothermal aging process can offer guidance for attaining superior magnetic performance in the temperature range from 25 to 500 °C for Gd-substituted Sm₂Co₁₇-type magnets.