Grain-size effect on the magnetoresistance peaks in thin nickel films

We report for the first time the grain-size effect on a newly measured angl e dependence of the MR (magnetoresistance) in thin nickel films. Were, the angle refers to the angle between the magnetic field and the film surface. We find that the angle dependence of the FDMP(magnetic field difference bet ween the two MR peaks) in thinner films less than 400-Angstrom thick is wel l explained using a function of 1/cos theta which can be obtained from the concept of the effective field in magnetization. However, in thicker films, the FDMP's rate of increase as a function of the angle is found to become faster than 1/cos theta. This different behavior of the angle dependence be tween thinner and thicker films is considered to be related to both grain f ormation and grain size in the films. Consequently, due to the different gr ain configuration, randomization of the magnetization vectors during the re versed magnetic field process in thicker films might be achieved through a three-dimensional process while in thinner films this is achieved through a two-dimensional process.