Ferromagnetic quantum dots formed by external laser irradiation

We present an efficient method for the formation of cobalt ferromagnetic quantum dots (FMQDs) by exposing a Nd: YAG laser (wavelength=355 nm) on ferromagnetic thin films grown on Si substrates. Primary emphasis is placed on the simple and direct fabrication of the FMQDs without performing any micro- or nanopattering process. Scanned laser irradiation of low power causes localized segregation of ultrathin as-deposited films by the laser-induced heat, resulting in the fabrication of FMQDs. Observations by scanning electron microscope and atomic force microscope clearly confirm highly uniform controllable nanoscale FMQDs in our case. The average size and density of the FMQDs were about 10 nm and 2×1011/cm2, respectively. Magnetic characteristics of the FMQDs were also measured by a superconducting quantum interference device at 5 K.