24 August 2006 Photo-magnetism and possible optical switching in Fe3+: PMN-PT: a Photo-EPR investigation
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Electron paramagnetic resonance (EPR) under the conditions of in situ laser illumination of the sample in the microwave cavity, called photo-EPR is an excellent method to detect photo induced electron transfer in real time. We report Photo- EPR results on the formation of clusters of magnetic ions in 0.67Pb(Mg1/3Nb2/3)O3. 0.33PbTiO3 (PMN-PT) on illumination with blue laser at room temperature .The Photo EPR signal with g=2.00, agrees with Pb3+ formation. The PMN-PT crystals 2-6mm size grown using PbO flux method were clear and transparent: and the upper part of the melt yielded pink colored crystals containing a few hundred PPM of Fe3+ as seen by EPR Signal at g=4.3. The large linewidth (~45 Gauss) of the photo-EPR signal and the presence of Fe3+ in the sample suggests the possibility of magnetic ion cluster formation on blue laser excitation. When the photo-magnetic centers were produced in magnetic field of 7.5KG, the signal was 30% more than that produced under switch-OFF condition of magnet having a remnant field of only 50G. This critical observation is a clear pointer to the formation of photo-induced magnetic polarons at room temperature, which are essentially clusters of ferromagnetically, coupled Fe3+ , Pb3+ and trapped electrons. The cluster formation and decay exhibited fast optical response with growth and decay time less than or equal to 100msec. These observations show that PMN-PT having excellent electromechanical properties can also be used for photomagnetic switching and real time holography with fast grating response using Pb2+ <--> Pb3+ process. PMN-PT would have additional advantage compared to other photo-refractive materials: due to possibility that the grating contrast can be manipulated by external magnetic field.
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Sundar Bairavarasu, Sundar Bairavarasu, M. E. Edwards, M. E. Edwards, M. D. Sastry, M. D. Sastry, F. Kochary, F. Kochary, D. Lianos, D. Lianos, M. D. Aggarwal, M. D. Aggarwal, } "Photo-magnetism and possible optical switching in Fe3+: PMN-PT: a Photo-EPR investigation", Proc. SPIE 6314, Photorefractive Fiber and Crystal Devices: Materials, Optical Properties, and Applications XII, 631409 (24 August 2006); doi: 10.1117/12.701456; https://doi.org/10.1117/12.701456

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