Magnetic and magneto-optic properties of bismuth-substituted thulium iron-garnet films

The saturation magnetization Ms, the uniaxial anisotropy constant Ku, and the Faraday rotation θF of epitaxially grown garnet films of composition Tm3−xBixFe5−yGayO12 were investigated for 0≤x≤0.83 and 0≤y≤1.57. The Bi content of the films was controlled by the melt composition and supercooling. The low-temperature saturation magnetization is determined by the antiparallel alignment of the Tm sublattice magnetization, and the increase of the Curie temperature is controlled by the bismuth content. No compensation temperature was observed due to the small Tm moment, in agreement with literature data. The uniaxial behavior of these films is associated with the stress-induced anisotropy increasing linearly with the lattice mismatch. The growth-induced part turned out to be negligible. The strong enhancement of the Faraday rotation compares well with that observed for other Bi-substituted iron garnets, yielding a contribution of θF = −1.9 × 106 deg/m at λ=633 nm and T=295 K. The temperature dependence of Ms and θF (λ=633 nm) was measured in the temperature range 4.2 K≤T≤TC. It agrees well with the calculated temperature variation based on the molecular-field theory.