Villarraga-Gómez, Herminso

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    Magneto-optical studies of Co-doped NiO thin films
    (2010) Villarraga-Gómez, Herminso; Jiménez-González, Héctor J.; College of Arts and Science - Science; Radovan, Henri; Singh, Surinder; Department of Physics; Colón-Ramírez, Silvestre
    In this work, we carried out magneto-optical measurements on transparent insu- lating thin films. We used a monochromator with a Xenon lamp source to generate monochromatic linearly polarized light. Combining this source with sensitive polar- ization modulation techniques enabled us to obtain magneto-optical spectra for the thin films. For this thesis, the focus is on Magnetic Circular Dichroism (MCD) and Faraday rotation. As the material to study we used several samples of Co-doped NiO thin films deposited through the spin-coating technique on quartz substrates. The spectral and temperature dependence of the magneto-optical phenomena for each of the Co-doped NiO thin films was studied in the energy region from the UV to the visible. After an extensive and meticulous study, we found that Co-doped thin films NiO did not exhibit any of the magneto-optical effects we attempted to measure: MCD and magnetic birefringence (Faraday rotation) in the wavelength range between 200 nm to 600 nm. However, we could not effectively explore MCD for wavelengths below 350, because of the high experimental dispersion caused by a low system optical throughput. The energy gap usually reported for NiO is ∼4 eV, corresponding to a wavelength of about 310 nm. Apart from the negative results obtained in out measurements, we learned some interesting lessons to keep in mind for future measurements in our laboratory, such as the existence of background effects produced by the whole optical system at zero applied magnetic field, which need to be eliminated in the computations. Some of these effects are sensitive to variations of the magnetic field on the quartz substrate. These effects must be taken into account in any attempt to measure MCD on thin films, in order to identify the response of the sample itself.