Critical exponents of GdCl 3, a ferromagnet with long-range interactions

Magnetization measurements on GdCl ₃, a 3-dimensional ferromagnet ( T_c = 2.210 ₅ K) with a weak isotropic Heisenberg exchange and dipole-dipole interactions of the same order of magnitude, yield crititcal exponents of β = 0.418 ± 0.007, γ = 1.078 ± 0.01, δ = 3.53 ± 0.05. They satisfy Widom's equality β( δ - 1) = γ but differ appreciably from values of systems with dominating short-range interactions. The results are compared with theories of larkin et al. (1969) and Fischer et al. (1972) for ferromagnets with long-range interactions.