FARADAY-ROTATION OF BISMUTH SUBSTITUTED TERBIUM IRON GARNETS

The spontaneous magnetization and the Faraday rotation PR, of [110]-or iented single crystal of composition BixTb3-xFe5O(12) with x=0.60 have been investigated as a function of temperature and compared with bism uth-free terbium iron-garnet. The experimental data, obtained at 1150 nm wavelength in the 10-300 K temperature range, are discussed in term s of electric and magnetic dipole transitions within the three magneti c sublattices, Assuming that the contribution of Be Fe3+ ions to FR is the same as bismuth-substituted yttrium iron garnet (for identical Ri content), the contribution to FR of the Tb dodecahedral ion exhibits a strong reduction induced by the bismuth incorporation. A strong temp erature variation of the Ist order electric dipole coefficient for the rare earth is found; in a first approximation, this coefficient prese nts a linear temperature dependence in the 100-300 K temperature range as previously observed in the pure TblG.