MAGNETIC AND MAGNETOOPTIC PROPERTIES OF BISMUTH-SUBSTITUTED THULIUM IRON-GARNET FILMS

The saturation magnetization M(s), the uniaxial anisotropy constant K(u), and the Faraday rotation theta-F of epitaxially grown garnet films of composition Tm(3-x)Bi(x)Fe(5-y)Ga(y)O12 were investigated for 0 less-than-or-equal-to x less-than-or-equal-to 0.83 and 0 less-than-or-equal-to y less-than-or-equal-to 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 theta-F = -1.9 X 10(6) deg/m at lambda = 633 nm and T = 295 K. The temperature dependence of M(s) and theta-F (lambda = 633 nm) was measured in the temperature range 4.2 K less-than-or-equal-to T less-than-or-equal-to T(C). It agrees well with the calculated temperature variation based on the molecular-field theory.