Structure and magnetic properties of Alnico8 alloy thermo-magnetically treated under a 10  T magnetic field

The structure and compositions of spinodal phases in Alnico8 alloy isothermally treated at 830 °C under external magnetic field (Hext) up to 10 T were investigated by transmission electron microscopy (TEM). Under ultra-high magnetic field (10 T), the spinodal structure of Alnico8 alloy presents interesting diversity for the shapes of α1 phase particles, namely, Π-shape, H-shape and Ш-shape apart from regular rod-shape. Composition analysis shows that the Fe was mainly distributed in the α1 phase. The Co content in the α1 phase was lower than that in the α2 phase as evidenced by the point analysis results, and Co content inα1 phase of the alloy treated without magnetic field was higher than that of the alloy treated with a magnetic field. In contrast, the Ni, Al, Cu and Ti were concentrated in the α2 phase. The average hyperfine field of the alloy treated without magnetic field was about 301.3 kOe. While the alloy treated under magnetic field, it was slightly decreased, which was about 292.0 and 296.1 kOe under 0.7 and 10 T, respectively. Magnetic properties of the alloy treated under a 10 T magnetic field were the best, which were about 1.09T, 396Oe and 9.5 kJ/m3 for Br, Hc and (BH)max respectively. Especially for the coercivity, which was mainly contributed by the anisotropy of the α1 phase induced by the high magnetic field. •High magnetic field (10T) increased the anisotropy of the α1 phase of the Alnico8 alloy isothermally treated at 830°C, obviously improved its magnetic properties.•When the alloy treated at 830°C under a 10T magnetic field, the magnetic properties of the alloy were the best.•The Co in the α1 phase of the alloy treated without magnetic field was higher than that of the alloy treated with a magnetic field.•The average hyperfine field of alloy treated with external magnetic field slightly deceased, compared to that of the alloy treated without magnetic field.