Enhancement of room temperature ferromagnetism in nanocrystalline Zr1-xMnxO2 by the suppression of monoclinic structure of zirconia

A series of nanocrystalline Zr1-xMnxO2 (0.005 <= x <= 0.02) samples were prepared by chemical route and further annealed at 750 degrees C for 5 h. All the prepared samples are in mixed phase of monoclinic and tetragonal form. However, the tetragonal phase of zirconia increases with the increase in Mn concentration and suppresses the monoclinic phase of zirconia. The bandgap the nanocrystalline samples decreases with the increase in Mn concentration, which confirms the substitution of Mn in zirconia matrix. The saturation magnetization increases with the increase in Mn concentration in nanocrystalline Zr1-xMnxO2. The occurrence of room temperature ferromagnetism in nanocrystalline Zr1-xMnxO2 is attributed due to the presence of oxygen vacancies and also due to the lattice distortion of ZrO2 by Mn substitution. The development of oxygen vacancies and the lattice distortion is well observed in Raman and Photoluminescence spectra. Again, the suppression of monoclinic phase and enhancement of tetragonal phase is the mechanism for the creation of oxygen vacancies for which the ferromagnetic contribution enhances with the increase in Mn concentration in nanocrystalline Zr1-xMnxO2.