Crystalline Electric Fields in Spinel-Type Crystals

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 (Li0.5Al2.5O4) which is isomorphous with lithium ferrite (Li0.5Fe2.5O4). 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 gII=2.006±0.002 were obtained. The magnetocrystalline anisotropy of Li0.5Fe2.5O4 was interpreted on the basis of the crystalline electric field parameters measured in the aluminate.