High-temperature magnetic properties of TbCu7-type SmCo-based films

In applications where large remanent moments and energy products are required at elevated temperatures, SmCo-based permanent magnets provide the best properties. In addition to their high Curie points, these SmCo-based ordered phases of 1-5, 2-17, and the disordered 1-7 phase show large uniaxial anisotropies at elevated temperatures. We have now measured the high-temperature hysteresis properties of single-phase TbCu7-type SmCo-based permanent magnet films. Such single-phase samples have the advantage that optimal magnetic properties can be obtained from the as-sputtered films without any subsequent heat treatments. Normally bulk samples in this composition range form the two phase cellular structure whose magnetic properties are very sensitive to heat treatments. Single-phase TbCu7-type films of composition Sm13Co58Fe20Cu7Zr2 were sputter synthesized such that the crystallite c axes were oriented in the film plane. The net anisotropy field of the films remained larger than the maximum applied field of 18 kOe even at the highest measurement temperature of 460 °C. Thus all measurements were from minor hysteresis loops. The in-plane coercivity showed a monotonic decrease from 6.0 kOe at room temperature to 1.3 kOe at 460 °C. The in-plane remanent flux density decreased from 8.5 kG at 50 °C to 5.8 kG at 460 °C.