A novel type of reversal propagating at high speed

Switching of a magnetic film can be induced by a homogeneous easy-axis field H
e
below switching threshold and a large, locally applied hard-axis field H
h
. If H
h
is a step function in time, the magnetization inside the region of the hard-axis field rotates with negligible delay toward the hard axis while the region outside tries to establish a state of curled magnetization. As soon as the magnetization in this region rotates away from the easy axis, however, the easy-axis field H
e
exerts an additional torque which pushes the magnetization further toward the hard axis. The region of partial rotation, therefore, tends to become wider. By an indirect probing method, it has been observed that a wide wavefront, traveling at high speed, results. The speed at the center of this wavefront was typically 10
⁷
cm/s. In addition, the leading edge of this wavefront appeared to propagate more than five times as fast. The length travelled exceeded 250 mils. This experiment strongly suggests that the switching occurs by a special type of noncoherent rotation. A static model has been set up in an attempt to explain this effect theoretically.