Abstract
Neutron scattering studies have been performed on amorphous alloys for several concentrations bracketing the spin-glass-ferromagnetic multicritical point found from magnetization measurements. The amorphous structure factor has been measured to 4.0 , and changes considerably for near the multicritical concentration. For the most Mn-rich sample (), the small-angle scattering is well described by a single Lorentzian. The corresponding inverse ferromagnetic correlation length remains nonzero (less than 0.04 ) at all temperatures. For , the Lorentzian scattering profile persists. As is reduced, decreases to a value indistinguishable from zero and subsequently increases, as it should for a ferromagnet which evolves into a reentrant spin-glass. For progressively smaller , the scattering function at low temperatures shows increasing deviations from the Lorentzian form, and instead is consistent with a power law with . These results are very similar to those found in other alloy series which display both ferromagnetic and spin-glass behavior. We argue that this power-law form of the spin correlations in the reentrant phase provides an important clue to the nature of the ferromagnet—spin-glass transition and the reentrant state itself. This leads us to a detailed heuristic model for the phase diagram and phase-transition behavior, including the reentrant phenomenon. The model is based on a decomposition, via the frustration mechanism, of spin systems with exchange interactions of random sign, into spin-glass-like and ferromagnetic networks. Many of the experimental results are explained in terms of random-field effects which arise when the ferromagnetic and spin-glass order parameters are coupled together.
- Received 14 June 1983
DOI:https://doi.org/10.1103/PhysRevB.28.5160
©1983 American Physical Society