Amorphous to polycrystalline transition in Co<InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\mathsf{_x}$</EquationSource> </InlineEquation>Si <InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\mathsf{_{1-x}}$</EquationSource> </InlineEquation> alloy thin films

The transition from amorphous to polycrystalline microstructure has been studied in sputtered Co<Subscript> x </Subscript>Si<Subscript>1-x </Subscript> alloy films by structural, magneto-optical and Nuclear Magnetic Resonance measurements. For <InlineEquation ID="Equ3"> <EquationSource Format="TEX">$x \geq 0.76$</EquationSource> </InlineEquation>, Si is diluted into Co without significantly altering the polycrystalline microstructure, composed of a mixture of hcp and fcc grains. However, the fraction of Co atoms that contribute to the Nuclear Magnetic Resonance signal is found to decrease steeply (down to about 60<InlineEquation ID="Equ4"> <EquationSource Format="TEX">$\%$</EquationSource> </InlineEquation> at x=0.76) suggesting a microscopic segregation of a Si rich phase that induces a large degree of disorder. This is reflected in a harder magnetic behavior and a strong anisotropy dispersion. Below x=0.75, the transition to an amorphous microstructure results in a sudden increase in the fraction of Co atoms within a ferromagnetic phase, indicating the recovery of the microscopic homogeneity. Also a significant enhancement of the macroscopic magnetic anisotropy is found for amorphous films with compositions right below the transition. Within the amorphous phase a second regime of Si segregation appears characterized by a constant Co local environment and constant magnetic properties. Finally, for x=0.65 there is a significant Si enrichment in the Co environment and the films become non magnetic for compositions below this point. Copyright Springer-Verlag Berlin/Heidelberg 2004