Flux Reversal in Single-Crystal MnBi Films

Abstract

Single‐crystal MnBi films of thickness ranging from 2500 to 260 Å were grown epitaxially on mica substrates by vacuum deposition followed by a prolonged annealing procedure. The c axis of these films is perpendicular to the plane of the film. Magnetic hysteresis in the direction along the c axis has been measured by both the magneto‐optic method and the torque magnetometer technique. The hysteresis loop shows an abrupt decrease in magnetization as the field is reduced from positive saturation to a critical value. This critical field is positive in films thicker than 1200 Å. The coercive force of the films varies from 200 Oe to 2 kOe as film thickness decreases. The thickness dependence of magnetic hysteresis was also measured on a 2400‐Å film by repeated etching down to 1000 Å. The general characteristics are the same as measured on films of different prepared thickness. This thickness dependence of coercive force is in agreement with the theoretical result calculated from domain theory assuming a stripe domain configuration. The field required to saturate the films is 3.7 kOe and is approximately identical for all films. The dynamic flux reversal properties of these films were measured using a magneto‐optical technique. The switching coefficient S_w was found to be 0.067 Oe·sec. These experimental results suggest that the flux reversal in these films is not by domain rotation, but by the motion of the domain wall.