Growth and magnetic properties of MnO2&#8722;delta nanowire microspheres
  We report the synthesis of MnO2&#8722;delta microspheres using hydrothermal and conventional chemical reaction methods. The microspheres of MnO2&#8722;delta consist of nanowires having a diameter of 20-50 nm and a length of 2-8 micro m. The value of the oxygen vacancy delta estimated from the x-ray photoelectron spectrum (XPS) is 0.3. The magnetization versus temperature curve indicates a magnetic transition at about 13 K. It is found that a parasitic ferromagnetic component is imposed on the antiferromagnetic structure of MnO2&#8722;delta, which might result from distortion of the lattice structure due to oxygen vacancies. The magnetic transition temperature TN is about 10 K lower than that of the bulk MnO2 single crystal. 
J.B. Yang, X.D. Zhou, W.J. James (Graduate Center for Materials   Research and Departments of Physics and Chemistry, Univers...