KERR HYSTERESIS LOOP TRACER WITH ALTERNATE DRIVING MAGNETIC-FIELD UP TO 10 KHZ

A magneto-optical Kerr loop tracer for hysteresis loop measurements in thin films with field excitation frequency f(0) from 10 mHz to 10 kHz is described. A very high sensitivity is obtained by using an ultrabr ight light-emitting diode as a low-noise light source and a novel acqu isition process, The field is generated with a coil driven by an audio amplifier connected to a free-running oscillator. The conditioned det ector output constitutes the magnetization signal (M); the magnetic fi eld (H) is measured with a fast Hall probe, The acquisition electronic s are based on a set of sample-and-hold amplifiers which allow the sim ultaneous sampling of M, H, and dH/dt. Acquisition is driven by a pers onal computer equipped with a multifunction I/O board, Test results on a 120 nm Fe film on Si substrate are shown. The coercive field of the film increases with frequency and nearly doubles at 10 kHz with respe ct to dc. (C) 1997 American Institute of Physics.