Fabrication, characterisation and magneto-optical enhancement of thin film BiGa Dy iron garnet

This thesis describes the production of BiGa:Dy Iron garnet thin films by the processes of both pulsed laser deposition and r.f. magnetron sputtering. High quality films with large magneto-optical effects, perpendicular magnetic anisotropy, square hysteresis loops and smooth surfaces with small grain size have been produced by both methods from the same Bi_2_._3Dy_0_._8Fe_4_._0Ga_0_._9O_1_2 target. The optimised PLD conditions required to produce films of maximum MO activity onto GGG(111) substrates included a substrate temperature of 590 deg. C and an oxygen pressure of 0.2mbar. Film composition exhibited the same stoichiometry as the target material. The films produced by r.f. magnetron sputtering displayed a low bismuth content, compared to those of the PLD films. Optimised conditions, including a post annealing temperature of 690 deg. C and an argon pressure of 0.04mbar, produced films of composition Bi_1_._2Dy_1_._3Fe_4_._4Ga_1_._1O_1_2. Optical and MO characterisation of both types of film, in terms of the intrinsic complex refractive index (n) and Voigt parameter (Q), throughout the visible region, revealed the increased Bi content harvested from the PLD process led to significantly larger optical absorption and MO effects. However, the sputtering technique produced films with superior surface quality, and film uniformity over a larger area. The optical and MO characterisation enabled the design and fabrication of multilayer enhancement structures to maximise the Kerr rotation, whilst minimising the Kerr ellipticity for a given reflectance value at a chosen wavelength. Large MO enhancement proved possible towards higher wavelengths ( > 500nm) where the absorption of the garnet was low, despite the much lower intrinsic MO activity displayed at these wavelengths. Temperature dependence measurements, carried out on garnet films, revealed that compensation temperature was very sensitive to film composition, and in particular, bismuth content. (author)Available from British Library Document Supply Centre-DSC:DXN026957 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo