MAGNETIC AND EPR STUDIES OF ALPHA-FE2WO6, BETA-FE2WO6, AND GAMMA-FE2WO6 PHASES AT LOW-TEMPERATURES

The polymorphic modifications alpha-, beta-, and gamma-Fe2WO6 of the i ron tungstate system were studied by means of magnetic susceptibility and EPR measurements at low temperatures. Both methods revealed a sign ificant paramagnetic contribution, probably resulting from local disto rtions of the antiferromagnetic bulk structure induced by a disturbed cation ordering or the presence of Fe2+ ions. The magnetic susceptibil ity revealed a peak at similar to 260 K for all samples which can be r elated with an AF phase transition. The EPR spectra comprised the cont ribution of various isolated paramagnetic iron centers, one arising fr om high-spin Fe3+ ions in rhombic crystal field symmetry with E/D appr oximate to 1/3 and D approximate to 0.22 cm(-1), an anisotropic EPR si gnal consistent with an S = 3/2 ground state with large zero-field spl itting, and a dominant component in the g approximate to 2 region pres umably arising from an S = 1/2 spin state. The latter spectra were ten tatively attributed to the formation of multi-iron clusters, one of th em invoking the presence of Fe2+ ions as well. For the beta-Fe2WO6 pha se an additional EPR spectrum was observed, which probably results fro m high-spin Fe3+ ions in a weak crystal field. (C) 1995 Academic Press , Inc.