Enhanced microwave performance of cobalt nanoflakes with strong shape anisotropy

Co nanoflakes are synthesized through a low temperature hydrothermal method. The single-phased hexagonal close-packed Co nanoflakes have a diameter of several micrometers and a thickness about 80 nm. Magnetic hysteresis loops are quite different along different directions deviating from the nanoflakes plane, which shows Co nanoflakes have strong magnetic anisotropy. Flakelike morphology influence the performance of complex permeability in gigahertz frequency. Natural resonance peak happens at 5.74 GHz with the contribution of shape anisotropy. Multiple resonance phenomenon appears due to the exchange resonance effect, which makes Co nanoflakes a broadband candidate for microwave absorbing material. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3432441]