Exchange of Cr³⁺ in GdAlO₃

The fluorescence of Cr3+ in GdAlO3 has been measured as a function of temperature. It is found that the single-ion spectra may be interpreted by including Heisenberg-type magnetic interactions of the Cr 3+ ion with its neighbouring Gd3+ ions and also the magnetic interactions between the Gd3+ ions themselves. The effect of these interactions it to split the sharp Cr3+ fluorescent lines into four bands, the separations of which change little between 77°K and 4 2°K but decrease below the Néel temperature of GdAlO3. The values of the exchange constants JCr3+ - Gd3+ and JGd3+ - Gd3+ are found to be 2 3 cm -1 and -0 06 cm-1, respectively.