CRITICAL MAGNETIC SCATTERING FROM RBMNF3

Critical magnetic scattering of neutrons and sublattice magnetization have been measured for RbMnF3 in the vicinity of the Néel point. The following critical indices have been obtained: β=0.316±0.008, M∼(ΔT)β 0.6%<ΔT/TN<5% ν=0.724±0.008, κ1∼(ΔT)ν 0.04%<ΔT/TN<18% γ=1.397±0.034 χ∼(ΔT)-γ 0.04%<ΔT/TN<4%, where M is the sublattice magnetization, κ1 the inverse range parameter, and χ the susceptibility. ν and γ were obtained from the critical scattering assuming (1) the quasielastic approximation and (2) the existence of the parameter η in the cross-section formula as proposed by Fisher and discussed below. For ΔT/TN<0.1% the critical scattering exhibited a pronounced deviation from Lorentzian shape. Excellent agreement was obtained, however, using a cross section of the form (A/κ12+q2)1-η/2, where q is the momentum transfer relative to the (111) magnetic reciprocal lattice point. The best value of η, obtained by least-squares curve fitting, was 0.067±0.01. Analysis of the data for q≫κ1, where resolution corrections were negligible, gave the same result. It is to be noted, in addition, that the best values of ν and γ obey the relation γ=(2-η). © 1969 The American Institute of Physics.