Millimeter wave e.s.r. studies of ferric iron in perovskite-type oxides

The paramagnetic resonance spectrum of Fe 3+ in lead and strontium titanates has been studied at Q band and 70 GHz, and at temperatures down to 4·2 °K. The zero-field splittings have been measured directly giving values of 1·06±0·05 cm -1 for lead titanate at room temperature and 2·698±0·006 cm -1 for strontium titanate. The spectrum for lead titanate can be fitted to a spin Hamiltonian with g parallel = g perpendicular = 2·0, D = 0·53 cm -1 and a = 2·70+10 -2 cm -1 and a 20% increase in the zero-field splitting parameter is observed on cooling from room temperature to 77 °K indicating a small lattice deformation. A second transition, tentatively indentified as arising from a charge-compensated site having a zero-field splitting equal to 1·8±0·1 cm -1 , has also been observed. The spectrum for strontium titanate has been studied at 35 GHz and 70 GHz and it is found that the Hamiltonian parameters differ slightly from those previously determined from the 10 GHz spectrum, in that different g values are required and effects of terms in a and F are also observed.