Magnetic properties of randomly oriented cobalt nano dots prepared by external laser irradiation process

Magnetic properties of randomly oriented ferromagnetic cobalt nano dots were investigated as a function of dot diameter. Polycrystalline Co thin film of 1 ∼ 3 nm was at first grown on Si substrate by a magnetron sputtering method and then followed by an ultraviolet laser exposure on as-grown Co thin film in order to produce Co nano dots with different diameters. The Co dot size, density, and spacing (distance between dot and nearby dots) was intentionally controlled by initial deposition thickness under optimum laser conditions. Magnetic hysteresis and angle-dependent magnetization of Co nano dots were measured with superconducting quantum interference devices, a vibrating sample magnetometer and magnetic force microscopy. The observed results demonstrate that the coercivity, hysteresis loops, reversal mechanism and anisotropy properties were strongly influenced by the exchange interaction with neighboring ferromagnetic nano dots.