Magnetic Properties and Microstructure of Sm 5Fe 17-Based Composite Magnets

We have investigated synthesis, magnetic properties and microstructure of Sm5Fe17-based hard magnetic phase with a Sm20Fe70Ti10 composition. Ultrahigh coercivities, μ0Hc=7.18 T at room temperature and μ0Hc=8.86 T at 10 K, have been achieved. The room-temperature coercivity, determined from high-field pulse measurements, reaches 35% of the anisotropy field μ0Ha=20.7±0.8 T. Further, it is demonstrated that a coercivity of 2.18 T is maintained even at 500 K. The Curie temperature TC of Sm20Fe70Ti10 is 577 K and the calculated exchange stiffness parameter A is 7.72 pJ/m. Detailed transmission electron microscopy investigations show a two-phase microstructure consisting of the Sm5Fe17-based hard magnetic matrix phase with grain size below 200 nm and finer, below 100 nm, Fe2Ti grains. Majority of the Fe2Ti phase is located at the grain boundaries with some finer inclusions found also inside the 5:17 grains. Despite the high fraction of the Fe2Ti grains, nearly single-phase demagnetization loops are observed. In order to enhance Ms, the effect of Ti content on phase constitution, magnetic properties and microstructure was studied in detail. Ms increases and Hc decreases for the Ti-lean compositions.