High-temperature Sm(Co, Fe, Cu, Ti)z permanent magnets

The effects of transition-metals such as Fe, Cu, Zr, and Ti substitutions in Sm-Co permanent magnets have been subject of thorough investigation for many years. Recently, they have found renewed attention in the context of high-temperature permanent magnets. For example, Ti-substituted Sm2Co17-type permanent magnets have excellent high temperature magnetic properties with H-c = 12.3 kOe at 500 degreesC. In this paper it is investigated how Fe and Ti affect the magnetic properties of sintered Sm-Co magnets by varying the Fe content of Sm(Co, Fe, Cu, Ti)(z) samples. A coercivity of 10.8 kOe at 500 degreesC has been achieved for a transition-metal ratio of 7.3. In combination with the positive effect of the Fe on the magnetization, this coercivity makes the material a promising candidate for high-temperature applications. Higher transition-metal ratios cause the coercivity to drop, as expected from the phase structure of Sm-Co magnets. The temperature dependence of the coercivity is explained in terms of the temperature dependence of the magnetic properties of the grain-boundary phase. TEM is used to investigate the difference between Ti-containing and ZT-containing magnets. Both compositions exhibit the cellular microstructure characteristic of sintered Sm-Co magnets, with cell sizes of about 100 nm. The main difference is the absence of the lamellar phase in the Ti-containing samples.