Magnetic field-induced off-resonance third-order optical nonlinearity of iron oxide nanoparticles incorporated mesoporous silica thin films during heat treatment

Highly dispersed and uniform Fe₂O₃ nanoparticles (NPs) have been incorporated into the pore channels of SBA-15 mesoporous silica thin films (MSTFs). And such Fe₂O₃ NPs incorporated MSTFs did not show detectable nonlinear optical (NLO) signals at off-resonance wavelength 1064 nm by Z-scan technique. However after a vacuum heat treatment at 800°C for 1 h under 6 T magnetic field, the Fe₂O₃ NPs incorporated MSTFs with very low Fe content (0.8-1.5 at.%) presented distinctive NLO signals with χ⁽³⁾ value in an order of 10 ^-10 esu. We proposed the physical reason for the NLO property generation to be the magnetic domain orientation of the iron oxide NPs incorporated within the pore channels of the MSTFs by the magnetic field heat treatment.