Structural, vibrational and magnetic properties of NiO-(Mg,Ti) powders: The effect of reduction reaction

We report a detailed structural, vibrational, and magnetic properties of mechanically alloyed NiO-(Mg,Ti) (x at. %) [x(Mg) = 0-50 and x(Ti) = 0-35] powders prepared using high-energy planetary ball mill under dry milling condition. Structural studies not only reveal a large crystallite size reduction during milling, but also illustrate an in-situ mechanochemical reduction of NiO with the reaction kinetics changing from gradual to self-sustaining type upon increasing x(Mg) and x(Ti). This yields a maximum NiO reduction of 95% and 73% for x(Mg) = 50 and x(Ti) = 35 with the formation of nanocomposites of NiO-Ni-MgO and NiO-Ni-TiO2, respectively. As a result, antiferromagnetic behavior of pure un-milled NiO transforms into ferromagnetic one with increasing x. The progress of NiO reduction is demonstrated from both the structural studies and the change in magnetization at room temperature and temperature dependent magnetic properties at high temperatures.