A Mössbauer-Effect Study of Antiferromagnetic FeCl2·4H2O

Abstract
Measurements of the Mössbauer effect of 57Fe in single‐crystal and polycrystalline absorbers of ferrous chloride tetrahydrate, FeCl2·4 H2O, have been made from the Néel temperature (TN∼1.1°K) down to 0.4°K. The hyperfine field at the iron nuclei was 260±5 kG and the Fe2+ spins were shown to align at a small angle to the symmetry axis of the electric‐field gradient tensor and to make an angle of about 30° with the b axis, in confirmation of the conclusions drawn from susceptibility and quadrupole splitting data. The decrease in the effective magnetic field at the nuclei with increasing temperature was small. Near TN the linewidth became very broad owing to the slowing down of the electron‐spin fluctuations.