NEUTRON-SCATTERING STUDY OF THE RANDOM-EXCHANGE ISING SYSTEM FEXZN1-XF2 NEAR THE PERCOLATION-THRESHOLD

Neutron-scattering measurements at H=0 in the dilute Ising antiferromagnet FexZn1-xF2, with x=0.25 and x=0.27, both concentrations above the percolation threshold x(p)=0.24, show no long-range order upon cooling to T=2 K. For temperatures above the equilibrium boundary T(eq)(H), measured previously in magnetization studies of FexZn1-xF2 for x=0.25, the scattering line shapes at H=0 are adequately described by Lorentzian functions, whereas below they are better described by the sum of a Lorentzian and a squared Lorentzian. The linewidths above T(eq)(0) decrease with T as if approaching a phase transition, at T almost-equal-to 12 K for x=0.27 and lower for x=0.25, but become limited at T(eq)(0). We will discuss these results in the context of other observations of spin-glass-like behavior observed in FexZn1-xF2 for 0.25 less-than-or-equal-to x less-than-or-equal-to 0.31. Comparison is made to an isomorphic, weakly anisotropic antiferromagnet and to Ising antiferromagnets with competing interactions.