Magnetic properties and giant magnetoresistance of Fe/Au multilayers

Abstract

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; dFe and dAu. For small dFe, the perpendicular magnetic anisotropy is induced, and in the films of dFe≈5 Å, the stripe magnetic domain patterns are observed. In dFe⩽3 Å, however, a superparamagnetic nature and a granular-type giant magnetoresistance (GMR) appear at room temperature. In a series of [Fe(3 Å)/Au(dAu)]40 MLs, the MR ratio increases with dAu and reaches the first peak at around 10 Å. 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 dAu≈10 Å. The layered structure is obscured and the superparamagnetic Fe grains are created by annealing at 300–350 °C, followed by the crystalline growth upon annealing at temperatures above 350 °C. These variations in the film morphology cause the changes in the saturation magnetization and the MR ratio.