Magnetic properties and giant magnetoresistance of Fe/Au multilayers

Magnetic properties and magnetoresistance (MR) are examined for the Fe/Au multilayers (MLs) prepared on glass substrates by electron-beam evaporation techniques as a function of the thicknesses of Fe and Au layers: d(Fe) and d(Au). For small d(Fe), the perpendicular magnetic anisotropy is induced, and in the films of d(Fe)approximate to 5 Angstrom, the stripe magnetic domain patterns are observed. In d(Fe)less than or equal to 3 Angstrom, however, a superparamagnetic nature and a granular-type giant magnetoresistance (GMR) appear at room temperature. In a series of [Fe(3 Angstrom)/Au(d(Au))](40) MLs, the MR ratio increases with d(Au) and reaches the first peak at around 10 Angstrom. On the other hand, at 14 K, the ferromagnetic component having a perpendicular anisotropy becomes dominant, and the GMR arises from the random wall alignment due to the antiferromagnetic coupling between the adjacent Fe layers, causing the first MR peak at d(Au)approximate to 10 Angstrom. The layered structure is obscured and the superparamagnetic Fe grains are created by annealing at 300-350 degrees C, followed by the crystalline growth upon annealing at temperatures above 350 degrees C. These variations in the film morphology cause the changes in the saturation magnetization and the MR ratio. (C) 1997 American Institute of Physics. [S0021-8979(97)01121-3].