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Finite-size effects in amorphous Fe90Zr10/Al75Zr25 multilayers

The thickness dependence of the magnetic properties of amorphous Fe90Zr10 layers has been explored using Fe90Zr10/Al75Zr25 multilayers. The Al75Zr25 layer thickness is kept at 40 Å, while the thickness of the Fe90Zr10 layers is varied between 5 and 20 Å. The thickness of the Al75Zr25 layers is sufficiently large to suppress any significant interlayer coupling. Both the Curie temperature and the spontaneous magnetization decrease non-linearly with decreasing thickness of the Fe90Zr10 layers. No ferromagnetic order is observed in the multilayer with 5 Å Fe90Zr10 layers. The variation of the Curie temperature $T_c$ with the Fe90Zr10 layer thickness $t$ is fitted with a finite-size scaling formula $[1-\Tc(t)/\Tc(\infty)]=[(t-t')/t_0]^{-λ}$, yielding $λ=1.2$, and a critical thickness $t'=6.5$ Å, below which the Curie temperature is zero.