Memory Effects In Manganese Perovskites
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HH2.9.1
Memory Effects In Manganese Perovskites N. Noginova, G. Chelule, G. B. Loutts Center for Materials Research, Norfolk State University, Norfolk, VA 23504 ABSTRACT Manganese doped perovskites are promising materials for non-magnetic data storage. Systems with low doping concentration, such as Mn:YAlO3 are high-quality optical crystals, demonstrating significant photorefractive effect. Optically and electrically induced quasi-permanent change in low-field conductivity was observed in the materials with high concentration of manganese such as single crystals and films of LaGa1-xMnxO3 (x= 0.1 – 1). These memory effects can last for a long time at room temperature and can be easily erased by heating up to 230 C. We explain our experimental results by photoinduced or thermoinduced local phase transition with the oxidation of Mn ions.
INTRODUCTION Manganese doped perovskites are promising materials for non-magnetic data storage. Systems with low doping concentration, such as Mn:YAlO3, Mn:YbAlO3 and Mn:GdAlO3 are high quality optical crystals, demonstrating significant photorefractive effect induced by light illumination at 550 nm or shorter wavelengths [1-4]. The effect is non-local, with maximum diffraction efficiency of 53% obtained at 514 nm in Mn:YAlO3 Changes in color and photorefractive index are quasi-permanent, lasting for many years at room temperature, and completely erasable by heating the crystal up to ~ 230 C. Holographic sensitivity in Mn:YAlO3 is strong enough and comparable with that in LiNbO3. Mn doped aluminates show promise for holographic recording and data storage in the visible and infrared regions, including two-color holographic recording scheme [5]. In these systems, Mn ions enter Al sites in the valence state 4+, or rare earth metal sites as Mn2+. The nature of photoinduced effects in these materials is related to the twostep photoionization of Mn4+ ions to the Mn5+ valence state. Based on the PDDT (photoexcitation, drift, diffusion and trapping) model, non-local photorefractive effect can be explained in terms of the redistribution of the photoexcited carriers and modulation of the electric field which causes modulation of the refractive index through linear electro-optical effect [6]. To increase the sensitivity and data storage capacity, it would be advantageous to use materials with high concentration of Mn ions. However, yttrium aluminates allow only a very low doping concentration of Mn of about 0.1%. Systems of LaGaO3 of a very similar to YAlO3 structure (space group Pbnm) are much more favorable to Mn doping. The ionic radius of Ga3+ is practically the same as that of Mn3+, so the doping concentration potentially can reach any desired level. From the other point of view, Mn3+ is a strong Jahn-Teller (JT) ion, thus one can expect the specific effects and specific distortions in the crystal lattice related to the presence of Jahn-Teller Mn3+ ions.
HH2.9.2
EXPERIMENT In the experiment, we study single crystals of LaGa1-xMnxO3 in the broad range of Mn concentrations, 0< x0.1 were s
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