Dipolar interactions at ferromagnetic critical points

The critical behavior for T>Tc and H=0 of ferromagnets with both isotropic exchange coupling and dipolar interactions is studied by exact renormalization-group techniques in d=4-ε dimensions (ε>0) with (n=d)-component spins. A crossover from short-range isotropic (Heisenberg) to characteristic dipolar behavior occurs. The asymptotic spin-spin correlation function develops a factor δαβ-qαqβq2 which suppresses longitudinal fluctuations. Experiments on EuO and EuS are considered.