Microstructural and electromagnetic properties of MnO2 coated nickel particles with submicron size

Nickel particles with submicron size are prepared by using the solvothermal method. These spheres are then coated with a layer of MnO₂ using the soft chemical method. The microstructure is characterized by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Energy x-ray dispersive spectrometry and high-resolution images show that the granular composites have a classical core/shell structure with an MnO₂ superficial layer, no more than 10~nm in thickness. The hysteresis measurements indicate that these submicron-size Ni composite powders have small remanence and moderate coercivity. The electromagnetic properties of the powders measured by a vector network analyzer in a frequency range of 2--18~GHz are also reported in detail.