Small-angle neutron scattering study of a magnetically inhomogeneous amorphous alloy with reentrant behavior

Abstract

Small-angle neutron scattering (SANS) measurements have been performed on an archetypal reentrant amorphous ferromagnet Fe{sub 91}Zr{sub 9} over the Q range 0.003 A{sup -1}<Q<0.2 A{sup -1} and temperatures between 10 and 300 K at fixed values of magnetic field H=0, 0.26, 0.5, and 4 T. Contrast matching experiments have also been carried out at room temperature before and after immersing the ribbons in deuterium oxide. The results of these experiments demonstrate that the surface effects tend to be important only for Q<0.006 A{sup -1}. Application of a field H=4 T much larger than that corresponding to the technical saturation of magnetization allows an unambiguous separation of the nuclear and magnetic scattering contributions to the measured SANS intensity. The standard practice of analyzing the Q-dependence of the SANS intensity of reentrant ferromagnetic systems in terms of the expression, Lorentzian plus Lorentzian-squared, revealed that in the present case, this expression fails to adequately describe the observed variation of the magnetic component of the SANS intensity with Q, even in the reentrant state. By comparison, a model, in which spin clusters of average size (R{approx_equal}2 nm) with a relatively narrow size distribution coexist with clusters of larger average size and wider size distribution,more » reproduces the magnetic scattering over the entire Q range at all temperatures. While the size of the smaller clusters does not change with temperature, the larger ones grow as the temperature is increased from the reentrant state at low temperatures up to the Curie temperature (T{sub C}) through the ferromagnetic regime. The present results also strongly indicate the presence of clusters at temperatures well above T{sub C} in the paramagnetic state.« less