Optically tunable magnetoresistance properties in La_0.7Sr_0.3MnO₃-Glass nanocomposites: A step towards Optospintronics

Perovskite manganites are interesting materials in spintronic devices due to their significant magneto-transport properties. Here, magneto-transport study has been carried out on structurally characterized (100−x) % La_0.7Sr_0.3MnO₃-x%Glass composites (x = 0(S1), 0.2(S2), 0.5(S3)). Our experiments provide evidences of largest MR (17%) for S2 sample, whereas 2% and 12% for S1 and S3 samples, respectively. Experimental MR vs H curves have been fitted employing a phenomenological model (Raychaudhuri et al. in J. Appl. Phys. 84:2048–2052, 1998) which indicates that it is the spin polarized tunnelling MR, which get modulated as a function of glass content. The surface spin susceptibility ^χ_b exhibits similar crossover behaviour with glass content in the composite. Such intriguing correlation of glass content dependence of ^χ_b and MRspt strongly suggest that ^χ_b i.e., the second order tunnelling across the interfacial region between adjacent LSMO grains governs SPT process and hence non-monotonic variation of MRspt with glass content. Optical tuning of SPTMR in the samples has also been investigated by 660 nm red laser light illumination. Non-monotonic photo-response exhibiting maximum photocurrent in S2 sample has been attributed to glass content ratio dependent exciton dissociation at interfacial region. Under illumination, decoherence and misalignment of surface spins seem to result in decrease in SPT magnetoresistance. Interfacial region of S2 sample has been found to be highly sensitive to optical illumination in which both χ_b and MRspt have been observed to switch their values from negative to positive ones. Large MRspt and switching of sign of MRspt with light illumination propose S2 nanocomposite as potential candidate for future Optospintronics applications.