A M ssbauer effect study of the magnetic properties of FeCl2.2H2O

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Abstract
The Mössbauer absorption spectrum of 57Fe in single crystals of FeCl2.2H2O has been studied. In the paramagnetic state the b axis is found to be the symmetry axis z of the crystalline electric field, and the quadrupole splitting is +2.63 mm sec-1 (½eQV zz/h = +30.6 Mc/s) at 77 °K. The orbital ground state of the Fe2+ ion is |xy, referred to the directions of the ligands as axes, and there is an excited orbital state |xz at 520 cm-1. In the antiferromagnetic state the hyperfine field is 255 kG and the axis of spin alignment is shown to lie in the ac plane close to the direction of the short Fe-Cl bond (the x axis), in agreement with susceptibility data. The asymmetry of the electric field gradient is given by η = (Vxx - Vyy)/Vzz = 0 2. By considering the effect of spin-orbit coupling on the orbital ground state the value of the quadrupole splitting and the g values may be satisfactorily understood.