Mathematical models for loss measurements in thin permalloy films with ramp drives

Uniaxial thin Permalloy films are driven with a large amplitude sinusoidal
H
field in order to approximate a ramp drive. The
H
field is characterized by rise times which exceed
3 \times 10^{6}
Oe/s. Two mathematical models are suggested to represent the loss measurements obtained in a domain wall motion region and in an incoherent rotation region. A normalized loss threshold is determined which characterizes the transition between the two regions. In the slow reversal or wall motion region, the normalized losses are proportional to the square root of α where
H = \alpha t
. In the relatively fast reversal or incoherent rotation region, the normalized losses are proportional to α. In both cases the inverse switching time is proportional to the coercive force in excess of the static value. Experimental data verify the reasonableness of the mathematical models.