Spin-glass-like nature in Fe/DyFe multilayers

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Abstract
Fe/DyFe multilayers were prepared by radio‐frequency magnetron sputtering, where DyFe layers were amorphous and nonmagnetic at room temperature. When the Fe layer thickness dFe decreases, the crystallographic structure of the Fe layer changes from body‐centered‐cubic to amorphous at around 20 Å. At this critical thickness, the spontaneous magnetization and the Kerr rotation angle are nearly zero and the magnetization curve does not show hysteresis or saturation indicating its spin‐glass‐like or superparamagnetic nature. For dFe < 20 Å, the saturation magnetization and the Kerr rotation angle increase again due to the Fe‐rich‐DyFe amorphous alloy formed at the vicinity of the layer boundary with decreasing dFe. The perpendicular anisotropy increases with decreasing dFe because of the interfacial anisotropy Ks = 0.62 erg/cm2 in the crystalline region of dFe ≳ 20 Å.