FeCl2 in a transverse magnetic field : inequivalent behaviour of the two sublattices at 0 K

For the uniaxial antiferromagnet FeCl2, we study the elastic and magnetic effects at 0 K due to the magneto-elastic coupling introduced by the crystal field of the Fe2+ ions. In a magnetic field H perpendicular to the easy magnetization axis, which is the 3 axis of the point group (3 m) of Fe2+ ions, strains occur destroying the crystal symmetry and a bulk magnetization appears with components along the field direction and also along the ternary axis. The presence of the component along the ternary axis is compatible with symmetry considerations. Also each of the magnetic moments of the two sublattices no longer lies in the plane defined by H and the ternary axis and they do not equally tilt towards the field direction. For H of a given size, the results vary quantitatively with the direction of H in the plane perpendicular to the ternary axis.