Small angle critical neutron scattering and the onset of ferromagnetism in Au-Fe alloys

Abstract

Small-angle neutron scattering measurements have been made on Au-Fe alloys as a function of temperature in the concentration range between 10 and 23 at.% Fe using cold neutrons of wavelength 6.7 AA. These reveal strong critical scattering peaks in alloys with 17 at.% and higher concentrations of Fe, whereas in alloys with lower Fe content the present measurements have failed to detect a similar behaviour. In these latter alloys, especially in the region around 15 at.% Fe, the neutron scattering results confirm the formation, with decreasing temperature, of large regions of correlated spins as inferred from the strong superparamagnetic behaviour observed in earlier magnetization measurements. The authors attribute the critical scattering in alloys containing 17 at.% Fe to the onset of ferromagnetism. The Curie temperatures thus obtained are discussed with reference to other measurements on this alloy system.