Photoinduced optical second-harmonic generation in Fe-Co-Si-B metallic spin glasses

Abstract

For the first time the second-order nonlinear optical effect has been observed in metallic spin glasses. Photoinduced second-harmonic generation (PISHG) in reflected light was used as a particular nonlinear optical method. We have varied the degree of long-range spin ordering detected by magnetoresistance measurements. PISHG is measured immediately after thermotreatment using thermoannealing (up to 823 K) of Fe18Co60Si9B13 glass. As a photoinducing beam a Q-switched nitrogen laser (λ = 337 nm) was used. A YAG:Nd pulse laser (W = 30 MW, τ = 30 ps, and frequency repetition of about 12 Hz) was applied as a probe. Only the presence of the photoexcitation stimulates the appearance of the PISHG with a value up to 0.128 pm V-1. The influence of the surface, phase matching conditions, fluorescence etc, is discussed. We have revealed an almost linear correlation between the degree of spin ordering and the PISHG output signal for different gaseous media. Molecular dynamics geometry optimization and self-consistent quantum chemical simulations have been performed. The observed phenomenon can be explained by contributions of long-range-ordered spins to electronic dipole moments determining second-order nonlinear optical susceptibilities.