Electric field dependence of a uniaxial anisotropy energy in lithium ferrite

By adapting a thermodynamic theory and method of measurement previously introduced for magnetite by two of the present authors, it is shown that at 77 °K the anisotropy energy of ionically ordered Li0.5Fe2.5O4 contains a component which is electric-field-dependent as well as shape-independent, and that it has uniaxial symmetry rather than the expected cubic symmetry. The magnetic field dependence of the magnetically induced electric polarization in zero electric field is predicted, and it is shown that in all but small magnetic fields this measured polarization is in good agreement with the proposed theory. Experimental evidence for the existence of a ’’skin’’ layer in Li0.5Fe2.5O4 crystals is also presented.