Magneto-Optic Indicator Films for Forensics
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Magneto-Optic Indicator Films for Forensics Charles Krafft1, Sergiy Tkachuk2, Garrett Lang2, David Bowen2, and Isaak. D. Mayergoyz2 1 Laboratory for Physical Sciences, 8050 Greenmead Dr., College Park, MD 20740, U.S.A. 2 Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, U.S.A. ABSTRACT Garnet films based on (BiPrGdLu) (FeGa) have been grown on (210) and (100) oriented SGGG substrates. (210) films with an easy plane of magnetization provided optimal imaging contrast. Incorporation of Au nanoparticles into an epitaxially grown film was done and these films show an increase in Faraday rotation, ostensibly due to the plasmon resonance effect. INTRODUCTION Magnetic fields have always held a mystical power, from the lodestone used by the ancient Greeks, and continuing to modern times with healthcare applications of magnetic resonance imaging. The ability to see this mystical force is likewise intriguing. First reported by Francis Bitter in 1931 [1] the use of magnetic particles dispersed in a colloidal suspension has remained a key tool for researchers to study magnetization patterns in magnetic materials. Over the years, various products have been developed to improve upon the colloidal suspension, however each had their limitations, be it particle size, sensitivity, or ease of application and use. During the 1990’s, magnetic garnet films were developed for the visualization of Abrikosov lattices in Type II superconductors [2]. Garnet films with planar magnetization and low coercivities when placed in close proximity to a magnetic field producing source were magnetized by this. The domain structure in the garnet was then visualized by the magneto-optic Faraday effect, in which the plane of linearly polarized light is rotated in the magnetic field, and in a direction that is field direction dependent. Thus, unlike the magnetic colloidal suspension, in which the ferromagnetic particles align along the magnetic flux lines without preference to polarity, the magnetic garnet provides means for observing the field as well as its polarity. Here, we report on an effort to develop a viable system to use garnets as a replacement for the magnetic colloidal suspensions in a forensics application. We will describe the desired magnetic and optical properties of the garnets, and then report on our research results for developing film compositions suitable for our application. We also report on an effort to increase the Faraday rotation in garnets films through a plasmon resonance effect. Gold nanoparticles are incorporated into the film during the epitaxial growth process. Results show a modest increase in the Faraday rotation in these gold-garnet films. THEORY Magneto-optical indicator films based on epitaxially grown iron garnet films are ideally suited for detection of two-dimensional magnetic patterns. The principle of operation of these
indicator films is based on the Faraday rotation of the plane of polarization of the linearly polarized transmitted light depending on an applied magnetic field
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