We have studied the influence of the stoichiometry on the structural, magnetic, and magneto-optical properties of bismuth iron garnet $\left({\text{Bi}}_3{\text{Fe}}_5{\text{O}}_{12}\right)$ thin films grown by pulsed laser deposition. Films with different stoichiometries have been obtained by varying the Bi/Fe ratio of the target and the oxygen pressure during deposition. Stoichiometry variations influence the Curie temperature $T_C$ by tuning the (Fe)-O-[Fe] geometry: $T_C$ increases when the lattice parameter decreases, contrary to what happens in the case of stoichiometric rare-earth iron garnets. The thermal variation of the magnetization, the Faraday rotation, and the Faraday ellipticity have been analyzed in the frame of the Néel two-sublattice magnetization model giving energies of $-48\text{K}$ (4.1 meV), $-29\text{K}$ (2.5 meV), and 84 K (7.3 meV) for the three magnetic exchange integrals $j_{aa}$, $j_{dd}$, and $j_{ad}$, respectively. Magneto-optical spectroscopy linked to compositional analysis by Rutherford backscattering spectroscopy shows that Bi and/or Fe deficiencies also affect the spectral variation (between 1.77 and 3.1 eV). Our results suggest that bismuth deficiency has an effect on the magneto-optical response of the tetrahedral Fe sublattice, whereas small iron deficiencies affect predominantly the magneto-optical response of the octahedral sublattice.

• Received 22 November 2007

DOI:https://doi.org/10.1103/PhysRevB.78.094429