Influence of coercive force and easy-axis bias on domain wall motion in NiFeCo films excited by hard-axis pulses

Domain wall motion in vacuum-deposited 1200 Å- 2000 Å-thick NiFe and NiFeCo films, excited by a 0.5 ns rise time/200 ns fall time hard-axis pulse field with an easy-axis dc field, is examined with regard to coercive force, easy-axis bias, and low-frequency creep results. Both NiFe and NiFeCo films have the same threshold field characteristics despite large differences in properties. The magnitude of the hard-axis pulse field necessary to cause creep increases with increasing difference between wall coercive force and easy-axis bias. Furthermore, the average creep displacement, for a given hard-axis pulse field magnitude, versus the easy-axis bias field normalized by wall coercive force results in almost identical curves for both NiFe and NiFeCo films except for a shift related to the threshold field. This result is consistent with previous low-frequency creep data and implies that the basic mechanism of low- and high-frequency creep may be closely related. The direction of the basic wall motion depends on the spin polarity in the wall and the durection of the hard-axis pulsed field. Motion in a direction opposite to the basic motion may be produced by an esay-axis bias field of sufficient magnitude but less than then wall coercive force, which is a new and significant result. A theory based on the dynamic torque equation and nonconservative spring coercive force model has been developed to explain the high-frequency creep phenomenon. This theory qualitatively predicts the observed experimental results very well.