Liquid phase epitaxy growth of bismuth-substituted yttrium iron garnet thin films for magneto-optical applications

Abstract

The novel Bi-substituted rare-earth iron garnet films were grown by the modified liquid phase epitaxy (LPE) technique for use as a 45° Faraday rotator in optical isolators. First, single crystals of Y 3Fe 5O 12 (YIG), with a lattice constant of 1.2378 nm, were grown by means of the Czochralski method. Using the seed crystal of YIG instead of the conventional non-magnetic garnet of Gd 3Ga 5O 12 as a substrate, a film of BiYbIG was grown by means of the LPE method from Bi 2O 3–B 2O 3 fluxes. The structural, magnetic and magneto-optical properties of BiYbIG LPE film/YIG crystal composite have been investigated using directional X-ray diffraction, electron probe microanalysis, vibrating sample magnetometer and near-infrared transmission spectrometry. The saturation magnetization 4πM s has been estimated to be approximately 1200 G. The Faraday rotation spectrum was measured by the method of rotating analyzer ellipsometry with the wavelength varying from 800 to 1700 nm. The resultant Bi 0.37Yb 2.63Fe 5O 12 LPE film/YIG crystal composite showed an increased Faraday rotation coefficient due to doping Bi 3+ ions on the dodecahedral sites of the magnetic garnet without increasing absorption loss, therefore a good magneto-optic figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved of 21.5 deg/dB and 30.2 deg/dB at 1300 nm and 1550 nm wavelengths, respectively, at room temperature. Since Yb 3+ ions and Y 3+ ions provide the opposite contributes to the wideband and temperature characteristic of Faraday rotation, the values of Faraday rotation wavelength and temperature coefficients were reduced to 0.06%/nm and 0.007 deg/°C at 1550 nm wavelength, respectively.