Sintering process effect on the magnetic behavior of vanadium-doped ZnO ceramics

V-doped ZnO ceramics were prepared using conventional sintering and spark plasma sintering from milled nanopowders. Prior to the sintering process, some powders were subjected to thermal treatment under reducing atmosphere in order to create oxygen vacancies. The sample sintered in air (with as-milled powders) exhibited the highest magnetization with a magnetic moment of 2.1 μ _B per V⁵⁺ ion and for a vanadium concentration of 4 at%. The samples sintered in vacuum or in Ar atmosphere (from reduced powders) exhibit lower magnetizations despite the formation of oxygen vacancies. Secondary phases were observed on these latest samples as the diamagnetic ZnV₂O₄ and the paramagnetic Zn₃(VO₄)₂ phases, which reduce the magnitude of the ferromagnetic signal. (paper)