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

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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.