Magnetic switching instability of ultrathin magnetic films under crossing pulse fields with duration shorter than relaxation time

We have studied the magnetization switching behaviour of ultra-thin films when we apply synchronous longitudinal and transverse pulse fields with duration shorter than relaxation time. The film was rectangular Permalloy with a dimension of 800 x 300 x 2 nm. In the case of a pulse duration of 100 ps, the switching map showed the c-shaped switching characteristics rather than the typical quasi-static asteroid. We found that the c-shaped switching characteristics are associated with the abnormal switching behaviour. The abnormal switching area was also found for a pulse duration of 300 ps and even in the precessional switching region for a pulse duration of 500 ps. Our results show that the transient non-uniform demagnetization developed by the crossing pulses is responsible for such abnormal switching behaviour, and this is supported by simulation for the elliptical film whose demagnetization field distribution is relatively uniform.