Millimicrosecond Magnetization Reversal in Thin Magnetic Films

From ferromagnetic resonance xperiments and from calculations based on the modified Landau-Lifschitz equation, switching times for the coherent rotation of the magnetization in thin, permalloy-type films have been predicted to lie in the range of 1 mi1limicrosecond.l First measurements by D. 0. Smith et a1,2 utilizing a travellingwave oscilloscope with a response time of 2 mpec, indicated switching times of about 3 mpec. In this communication, first results of advanced millimicrosecond measurements are reported. These were obtained by using special pulse equipment including a sampling oscilloscope,324 with an over-all response time of about 0.5 mpsec. Flux changes as fast as 1.5 m p e c could be observed, for not only the longitudinal flux component,5 but also, for the first time, the transverse one. Experimental techniques A pulsed magnetic field is generated in a 50-f2 shortcircuited strip transmission line by discharging a 50-0 coaxial cable over a coaxial mercury relay. The end of the cable is matched for the reflected wave by diodes and RC-compensating networks. Two pairs of Helmholtz coils provide the premagnetization and reset fields in the plane of the film. The longitudinal magnetic flux change of the magnetic film is picked up by a wire placed in the symmetry axis of the strip line. The end of this wire is matched by four balancing resistors (Fig. l a ) . By this means the voltage induced by the air flux is cancelled out. The transverse flux change of the film is picked up by a wire placed normal to the axis of the strip line (Fig. 1 b) .