Origin of Ferromagnetism in Cd1−xMnxO Nanoparticles

The origin of ferromagnetism in nanoparticles of polycrystalline Cd 1− x Mn x O ( x = 0, 2%, 10%) prepared using co-precipitation method is presented. The XPS studies indicate the presence of oxygen vacancies along with mixed oxidation states of manganese (Mn 4+ and Mn 2+ ) and cadmium (Cd 2+ , Cd 4+ ). The room temperature isothermal hysteresis measurements show that upon Mn doping, there is enhancement in ferromagnetic ordering and in coercivity of CdO nanoparticles. The zero-field-cooled and field-cooled magnetization as function of temperature indicates the presence of disordered magnetic structure, which may be due to the formation of bound magnetic polarons by mixed valance states of Mn cations and oxygen vacancies. The enhancement in dielectric constant with Mn substitution also points to the enhancement of space charge polarization and the frequency-dependent ac-conductivity indicates the small polarons hoping mechanism of conductivity.