Abstract
Mössbauer studies of antiferromagnetic FeCO3 below and above the Néel temperature show an asymmetric line broadening, and a constant value of 184 kOe of the magnetic hyperfine field from 0 to 12TN. These phenomena are explained using an Ising model with slow electron relaxation. The relaxation rate decreases with decreasing temperature, suggesting a spin-lattice relaxation. The Néel temperature was found to be (38.3±0.3)°K, which is 3.3°K higher than that measured by neutron diffraction.