Super-paramagnetic and unusual nonlinear absorption switching behavior of an in situ decorated CdFe2O4–rGO nanocomposite

Abstract

A simple strategy based on electrostatic interaction was utilized to assemble in situ cadmium ferrite of various morphologies (nanoplatelets to nanorods) on reduced graphene oxide sheets using a one-step hydrothermal reaction. With ultrafast laser excitation (800 nm, 150 fs and 80 MHz), intensity dependent open aperture Z-scan data confirmed the presence of nonlinear absorption in pure GO [saturable absorption] and CdFe₂O₄ [reverse saturable absorption]. Surprisingly, the nanocomposite exhibited unusual switching of reverse saturable absorption at low peak intensities (I₀ = 150 MW cm⁻²) to saturable absorption behavior at high peak intensities (I₀ = 250 MW cm⁻² and 350 MW cm⁻²). This unusual nonlinear absorption switching suggests the contribution of the individual components of the nanocomposite with respect to the intensity of excitation. All the samples exhibited nonlinear self-defocusing behaviour resulting from thermally-induced nonlinear refraction. High NLO coefficients were observed for the CdFe₂O₄⁻ (15 wt%) rGO nanocomposite which can be attributed to the synergetic effects stemming from the extent of conjugation with the graphene layers and 1D nanostructures of cadmium ferrite with a large reactive surface area for optical excitations. Earlier the different loadings and their respective morphologies were investigated by XPS, Raman, TGA, FESEM and TEM studies. Furthermore, the alteration in ground-state absorption and superparamagnetic properties with trimming was also analysed. Tunability of the thermal, magnetic, linear optical and NLO properties of the composites arises mainly due to tailoring the proportion of oxygen containing groups in the graphene layer and the CdFe₂O₄ loading on the graphene sheets, and the morphology of the CdFe₂O₄·CdFe₂O₄⁻ (15 wt%) rGO nanocomposite exhibits excellent optical limiting action, implying the potential possibility of it being used in laser safety devices.