The evolution of magnetic order in CrFe alloys. II. Onset of ferromagnetism

Abstract

For pt.I see ibid., vol.13, p.441 (1983). The magnetic phase diagram for CrFe alloys was determined by neutron scattering and low-field magnetisation. Two critical concentrations were found as the state of magnetic order evolved from itinerant antiferromagnetism for Fe concentrations less than cA=16.0+or-0.5% to ferromagnetism for Fe concentrations greater than cF=19.0+or-0.5%. Spin-glass behaviour was observed between the two critical concentrations. The onset of ferromagnetism was studied by neutron small-angle scattering. Analysis of the concentration and temperature dependence of the magnetic correlation range below cF suggested that a geometrical element is involved in the development of ferromagnetic long-range order; these results were in semi-quantitative agreement with models for the percolation multi-critical point. The bulk magnetic properties of alloys between the two critical concentrations were consistent with a simple fine magnetic particle model of percolation clusters of Fe moments fluctuating against barriers arising from magnetostatic shape anisotropy.