EXPERIMENTAL-STUDY OF MAGNETIZATION REVERSAL PROCESSES IN NONSYMMETRIC SPIN-VALVE

We have investigated a nonsymmetric bottom giant magnetoresistance spi n valve with the structure Si/NiO/Co/Cu/Co/Ta, as well as single ferro magnetic Co layers on antiferromagnetic NiO, with or without a nonmagn etic Cu spacer. Magnetic hysteresis loops have been measured by SQUID magnetometry, and magnetic domain structures have been imaged using an advanced magneto-optical indicator film (MOIF) technique. The MOIF te chnique demonstrated that the first stage of magnetization reversal is characterized by nucleation of many microdomains. With increasing rev ersed field, the domain walls move over small distances (5-20 mu m) un til annihilation. The domain size was observed to increase with the th ickness of the Co layer. When an alternating magnetic field was applie d, the domain structure was dramatically changed. (C) 1997 American In stitute of Physics.