Magnetic flux reversal in laminated Ni-Fe films

Anomalously fast flux reversal has been observed in films made of Ni-Fe layers separated by SiO. The speed of reversal increases as the number of identical layers of Ni-Fe increases. For a 5-layer film, the anomalous speed is observed in films with the SiO thickness as great as 1600 Å. Reversal time curves presented as a family of curves of1/tau = f(h_{perp})with hsas a parameter have two regions. The high-drive region has a lower slope in the laminated films when compared to the single-layer films. For this family of curves, a switching coefficientS_{w'}can be defined, as the inverse slope, in a manner similar to the definition of Swfor1/tau = f(h_{s})withh_{perp}as a parameter. For films with from two to five layers, Sw' is constant at1 times 10^{-3} mus and is smaller by an order of magnitude for the single-layer films. A dual loop experiment is used to confirm that coherent rotation is not a dominant mechanism. It is concluded that a model must satisfy the following criteria to successfully describe flux reversal in the laminated films: It must provide rapid flux reversal for fields less than Hk, an insensitivity to transverse fields either constant or pulsed, and an interaction that can survive over a wide range of SiO thicknesses.