Growth process and microwave absorption properties of nanostructured γ-MnO2 urchins

► We prepared urchinlike γ-MnO2 nanostructures by hydrothermal method. ► γ-MnO2 microspheres formed firstly and the nanoneedles grew subsequently. ► A rational growth mechanism was proposed. ► An effective absorption bandwidth of 8.8 GHz was achieved.