Cobalt nanoclusters in silica glass: Nonlinear optical and magnetic properties

Fused silica plates were implanted with Co ions at room temperature at the energy of 50 keV and to the fluence of 4×1016 ions cm−2. The formation of metal nanoclusters was observed by transmission electron microscopy. The cluster size distribution is narrow with a mean-diameter value of about 3 nm. Atomic in-depth distribution was determined by Rutherford backscattering spectrometry, whereas the cobalt chemical state was characterized by electron spectroscopies. Nonlinear refractive index n2 is of the order of 0.2 cm2 G W−1, as determined by the Z-scan technique at a wavelength of 770 nm for 130 fs long pulses at a 76 MHz repetition rate. Zero-field-cooled and field-cooled magnetization curves at the liquid-helium temperature exhibit features of superparamagnetic behavior that are characteristic of assemblies of single-domain nanoparticles.