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; $d_{\mathrm{Fe}}$ and $d_{\mathrm{Au}}.$ For small $d_{\mathrm{Fe}},$ the perpendicular magnetic anisotropy is induced, and in the films of $d_{\mathrm{Fe}}\text{≈5\hspace{0.17em}Å,}$ the stripe magnetic domain patterns are observed. In $d_{\mathrm{Fe}}\text{⩽3\hspace{0.17em}Å,}$ however, a superparamagnetic nature and a granular-type giant magnetoresistance (GMR) appear at room temperature. In a series of $[\mathrm{Fe(3\hspace{0.17em}\AA )/Au}{\mathrm{(d}}_{\mathrm{Au}}{\mathrm{)]}}_{40}$ MLs, the MR ratio increases with $d_{\mathrm{Au}}$ 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 $d_{\mathrm{Au}}\text{≈10\hspace{0.17em}Å.}$ 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.