Magnetic correlations in amorphous Fe-Zr alloys

Results of high-resolution small-angle neutron scattering (SANS) studies on amorphous alloys of composition Fe_xZr_100-x, x=90, 91, 92, show that ferromagnetic correlations exist below T_c, but that conventional long-range order is destroyed by competing exchange interactions. The transition temperatures drop with increasing iron concentration (T _c ≊226 K for Fe₉₀Zr₁₀ down to T_c ≊175 K for Fe₉₂Zr₈). Data taken at very low Q (0.008 Å^-1<Q<0.02 Å^-1) provide evidence of relatively large (≊200-≊400 Å) static spin clusters which do not disorder at T _c. Superposed on this is an ordering with a second shorter length scale which shows a cusp (not divergent) at the bulk T_c. The data were fitted to a combination of a Lorentzian and a power of a Lorentzian, the latter of which represents scattering from clusters with a Maxwellian distribution of sizes.