MAGNETIC VISCOSITY EFFECTS IN THE GIANT MAGNETORESISTANCE OF NIO PERMALLOY/CU/PERMALLOY EXCHANGE-BIASED FILMS/

We have examined the effects of magnetic viscosity (magnetic aftereffe ct) on the giant magnetoresistance (GMR) of NiO/Permalloy(45 Angstrom) /Cu(45 Angstrom)/Permalloy(45 Angstrom) exchange-biased spin-valve str uctures grown by direct current (de) magnetron sputtering on Si substr ates. One of the samples had a 6 Angstrom Co layer on both sides of th e Cu layer. GMR is a sensitive indicator of magnetic viscosity effects since any time dependence in the magnetization reversal of one of the layers is reflected directly in the GMR. Two different types of GMR m easurements were made over the temperature range of -30 degrees C to 5 0 degrees C. The maximum time for the resistance to stabilize to 1 par t in 10(4) ranged from about 70 to 200 s for both samples at the tempe ratures studied. The time dependency of the GMR was well described by C + S ln t, where S and C are constants; S is called the coefficient o f magnetic viscosity. This equation characterizes the classic time dep endent behavior of the magnetization. The maximum magnitude of S was f ound to decrease as the temperature was increased.