Crystalline Electric Fields in Spinel-Type Crystals

Abstract

Electron paramagnetic resonance (EPR) measurements are reported for the Fe³⁺ ion in long range “ordered” and “disordered” single crystals of the spinel-type compound lithium aluminate (Li_0.5Al_2.5O₄) which is isomorphous with lithium ferrite (Li_0.5Fe_2.5O₄). In the “disordered” aluminate most of the EPR linewidths were found to be very broad, whereas in the “ordered” aluminate the linewidths were comparatively narrow. The broadness of the linewidths in the “disordered” aluminate prevented quantitative determination of the crystalline electric fields in this state. From comparison of the “ordered” and “disordered” EPR linewidths, it was deduced that large fluctuations in the crystalline electric fields may exist in other “disordered” spinels also. In the “ordered” aluminate, the EPR spectrum was measured for the tetrahedral sites (which have trigonal symmetry), and the values |D| =0.104 cm⁻¹, |a−F| =0.0166 cm⁻¹, and g _II = 2.006±0.002 were obtained. The magnetocrystalline anisotropy of Li_0.5Fe_2.5O₄ was interpreted on the basis of the crystalline electric field parameters measured in the aluminate.