Photo-magnetism and possible optical switching in Fe³⁺: PMN-PT: A Photo-EPR investigation

Abstract

Electron paramagnetic resonance (EPR) under the conditions of insitu 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(Mg 1/3 Nb 2/3 )O 3 . 0.33PbTiO 3 (PMN-PT) on illumination with blue laser at room temperature .The Photo EPR signal with g=2.00, agrees with Pb 3+ 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 Fe 3+ as seen by EPR Signal at g=4.3. The large linewidth (~45 Gauss) of the photo-EPR signal and the presence of Fe 3+ 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 Fe 3+ , Pb 3+ and trapped electrons. The cluster formation and decay exhibited fast optical response with growth and decay time ≤ 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 Pb 2+ ↔ Pb 3+ 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.