Effect of light on the magnetic properties of cobalt ferrite nanoparticles

We report variations in the coercivity of CoFe/sub 2/O/sub 4/ nanoparticles as a function of particle size, temperature and light intensity. For 30 nm particles, this change in was 2300 Oe at 10 K, 120 Oe at 170 K, for a light intensity of under 2 milliwatts. The remanent magnetization was nearly unchanged by illumination. A simple model of optical absorption followed by electron transfer between Co/sup 2+/ and Fe/sup 3+/ ions is proposed.