Magnetic properties of cobalt nanodots fabricated by a new laser irradiation method: anisotropy and superparamagnetism

Superparamagnetic regions and magnetic anisotropic properties in randomly orientated Co nanodots (NDs) are investigated as a function of dot diameter. The Co NDs are fabricated by intentionally exposing a laser source on ultrathin Co film. Various dot sizes are ultimately realized by changing laser power, scan condition, and initial film thickness. Magnetic hysteresis loops and temperature dependence magnetization of the Co NDs are measured with a superconducting quantum interference device. The analysis of magnetization and hysteresis loops is effectively used to determine superparamagnetic regions of the Co NDs. The experimentally observed results repealed that room temperature superparamagnetic limit of our Co NDs was about 30 nm in diameter, with the confirmation of high resolution transmission electron microscope.