A Study of Magnetic and Electronic Correlations in Hydrogen-Induced Room Temperature Ferromagnetism in Co-doped ZnO

The effect of Co doping (5%) on the crystal structure, electronic structure and magnetic properties of poly-crystalline ZnO has been investigated using XRD, VSM, XPS and resistivity measurements. The study is aimed at correlating the observed changes in the magnetic behavior vis à vis changes in oxygen content, carrier concentration, absence of Co clusters etc. Rietveld analysis of XRD patterns confirms single phase crystallization in Wurtzite hexagonal structure (Space group: P63mc) with no evidence of any secondary phases. The as-prepared Co doped sample shows a paramagnetic state; however, upon hydrogenation it showed strong ferromagnetic ordering at 300 K. Interestingly, the Hinduced magnetic moment gets suppressed upon re-heating the sample in air and finally it becomes paramagnetic upon extended heating. The XPS results show that Co ions incorporate at Zn⁺² sites in +2 oxidation state with no evidence of metallic Co formation. The observed room temperature ferromagnetism (RTFM) is explained in terms of oxygen vacancies evolved as a result of hydrogen injection in Co doped ZnO lattice. The resistance also decreases for the hydrogenated sample, remarkably, confirming that additional carriers induced upon hydrogenation mediate the exchange coupling and contribute to the FM ordering