Structure and magnetic properties of TbCu7-type melt-spun Sm–Fe–B alloys

The melt-spun SmFe12Bx (x = 0, 0.50, 0.75, 1.00, 1.25 and 1.50) ribbons were prepared at 40 m·s−1, and their structure and magnetic properties were studied by powder X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM). XRD results indicate that SmFe12Bx alloys with 0.50 ≤ x ≤ 1.00 are composed of single-phase TbCu7-type structure. Moreover, it is found that the boron addition can inhibit the emergence of soft magnetic phase α-Fe and result in the increase in the axial ratio c/a. After annealing at 650 °C for 0.5 h, the metastable phase TbCu7 initially decomposes into the stable phase Sm2Fe14B (Nd2Fe14B-type) and α-Fe. The value of magnetic moment per Fe atom increases slightly from 1.75μB for boron-free sample to 1.80μB for the x = 0.75 sample and then decreases again. In addition, the best magnetic properties of maximum energy product [(BH)max] of 14.56 kJ·m−3, coercivity (Hcj) of 172.6 kA·m−1 and remanence (Br) of 0.45T are obtained for the SmFe12B1.00 alloy. Based on transmission electron microscopy (TEM) results, the average size of grains is around 197 nm for B-free sample and decreases to 95 nm for x = 1.00 sample, indicating that the addition of boron can refine grains.