CRYSTALLOGRAPHIC AND MAGNETIC-PROPERTIES OF 5(FE2O3)-3(AL2O3)-(GA2O3)-(SIO) BY MOSSBAUER-EFFECT

The structural and magnetic properties of 5(Fe2O3)-3(Al2O3)-(Ga2O3) -(SiO) have been investigated using Mossbauer spectroscopy and x-ray diffraction. The X-ray diffraction pattern shows that the crystal structure is of a cubic spinel type. The lattice constant (a = 8.324 angstrom) has been found by extrapolation using the Nelson-Riley function and it decreases slightly with Ga concentration although the Ga3+ ions are larger than the Al3+ ions, which can be attributed to a higher degree of covalency in Ga-O bonds than in Al-O and Fe-O bonds, which can also be explained with the help of the observed Mossbauer parameters. The zero-field Mossbauer spectra at 50K less-than-or-equal-to T less-than-or-equal-to 750K are various and anomalous as shown in Fig.2,3. The spectra at low temperature consist of two sextets which are identified to arise from Fe3+ ions at tetrahedral(A-) sites and octahedral(B-) sites, of two sextets and a doublet for R.T. less-than-or-equal-to T less-than-or-equal-to 600K. The central lines are asymmetric. This asymmetry can be ascribed to the preferred orientation of crystallites because of the temperature independence of the asymmetry.