Spin reorientation in melt-spun neodymium-iron-boron ribbons

Abstract

Effects of the spin reorientation in Nd2Fe14B below Ts =135 K on the hard magnetic properties of melt-spun Nd-Fe-B ribbons are reported. As the ribbons are cooled from room temperature, the shape of the second quadrant demagnetization curve is maintained down to 150 K, with an intrinsic coercivity Hci which increases steadily from 14 to 24 kOe. As the magnetic structure of Nd2 Fe14 B changes from easy axis to easy cone below 135 K, however, demagnetization occurs in two steps, with a large decrease in magnetization at low reverse field followed by a second sharp drop at higher field. The size of the initial drop correlates well with the canting angle of the cone and is consistent with having little or no resistance to rotation of the magnetization along the cone. This effect artificially suppresses Hci , which decreases to 23 kOe at 5 K. Magnetization reversal from one easy cone to the opposite cone remains a hard process, and its effective coercivity is estimated to be 42 kOe at 5 K. The first quadrant magnetization is much closer to full saturation at low fields due to the improved net alignment of the moments. In thermomagnetic scans this appears as a large increase in magnetization as the sample cools through Ts at constant field. The observed behavior agrees with that predicted by the known easy cone structure of Nd2 Fe14 B below Ts .