RESEARCH AND DEVELOPMENT OF THIN GARNET FILM BASED MAGNETO-OPTICAL IMAGERS.

Abstract

This dissertation deals with the use of magnetic single-crystal bismuth-substituted iron garnet thin films for magneto-optical imaging (MOI) of stray magnetic fields. The main advantages of such garnet-based imagers are their high sensitivity, high contrast and possibility to design films for imaging of magnetic fields in a wide range of magnitudes. The garnet films have been grown by the liquid phase epitaxy method from a flux melt on (210)- and (100)-oriented substrates and extensively characterized using various magnetic and optical methods. Specific melt compositions are identified that allow the growth of high sensitivity and high contrast indicator films on (210)-oriented substrates. Very low saturation field and high sensitivity of such garnet films are attributed to the existence of the so-called "easy plane of magnetization", a plane for which the magnetic free energy density is at a minimum for any orientation of the magnetization vector within this plane. Etching has been extensively used to investigate the effect of intrinsic film domain structures on the quality of MO imagers. It has been determined that the size of the domains reduces as the thickness of the film gets smaller. Below 1μm film thickness, the domains start evolving towards the "single domain" state which is beneficial for imaging purposes. The comparison of the imaging capabilities of the etched films grown on (210)- and (100)-oriented substrates has been performed and the resolution of the (100)-oriented imagers has been found to be inferior to the imagers based on the (210)-oriented samples with an easy plane of magnetization. The possibilities to enhance magneto-optic effects by strong local electric fields from optically induced plasmon resonances in gold nanoparticles embedded in garnet media are analyzed. The experimental investigation of the plasmon resonance enhancement of the Faraday effect has been performed and about 50% increase in Faraday rotation angle at a wavelength of 633 nm has been measured for the samples of interest. It is expected that under ideal conditions of the plasmon resonance excitation as well as proper garnet film parameters, an increase in Faraday rotation up to 400% could be achieved.