  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.
