The microstructure of the SmCo5 thin films sputter deposited on Cu underlayers was investigated to explain the high coercivity Hc. Energy filtered elemental map and energy dispersive x-ray spectroscopy line analysis showed that Cu diffused into the SmCo5 layer to form a Sm(Co,Cu)5 solid solution. Composition fluctuations with a scale length of 40 nm were found within the Sm(Co,Cu)5 layer, which would cause the local changes in the magnetocrystalline anisotropy. The high coercivity that was observed in the continuous Sm(Co,Cu)5 layer may be attributed to the pinning force for the magnetic domain wall motion due to the fluctuation of the magnetocrystalline anisotropy. The structure and magnetic properties of the SmCo5 thin film deposited on a Pt underlayer were also examined for comparison.
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