No abstract

The nanocomposites Sm–Fe–Ga–C with low Sm contents have been prepared directly by melt spinning without a subsequent heat treatment. A highly isotropic remanence to saturation magnetization ratio of 0.6–0.7 and a relatively high coercivity of 5.5 kOe were achieved from the as-quenched ribbons. X-ray diffraction and thermomagnetic analyses show that the as-quenched ribbons consist of a magnetically hard phase Sm2Fe15Ga2Cx and a magnetically soft phase α-Fe. Transmission electron microscopy observation demonstrates that the major 2:17-type phase has larger crystallites and the crystallites of the minor phase α-Fe are smaller and located separately at the grain boundaries of the major phase. The remanence enhancement is attributed to the exchange coupling between the intergrains. Both microstructure and magnetic properties are found to depend sensitively on the substrate velocity. The effect of the microstructure on hard magnetic properties has been discussed.

No abstract

The change in the magnetic properties of melt-spun Sm2+δFe15Ga2C2 permanent magnets with variation of the Sm content δ has been investigated in the range of −0.05⩽δ⩽0.20. A drastic increase in the coercive field μ0HC from 1.5 to 2.2 T at room temperature has been observed for δ⩾0.1. This can be understood as an influence of the Sm-rich nonmagnetic intergranular phase, occurring due to the Sm excess. Room temperature values of the maximum energy density up to (BH)max=64.2 kJ/m3 (δ=0.03) can be obtained. The samples with higher Sm contents exhibit larger values of the maximum energy density at elevated temperatures (T⩾450 K). For δ=0.13, a value of (BH)max=31.4 kJ/m3 has been observed at 500 K. The microstructural parameters αK and Neff describing the influence of the nonideal microstructure on the coercive field in the framework of the nucleation model were determined from the temperature dependence of the coercive field.

No abstract