Origin of ferromagnetism in Cu doped rutile TiO2 - An ab-initio approach

Origin of room temperature ferromagnetism in copper doped rutile TiO2 has been studied by varying both copper concentrations as well as oxygen vacancies. Ab-initio calculations have been carried out within the framework of density functional theory. Copper atom has been doped at two different positions to study the effect of distance between the dopants for ferromagnetism in TiO2 system. Spin polarized density of states calculation has been performed for each system and the induced magnetic moment has been calculated along with the total free energy and Fermi energy. Spin-spin interaction studies have been performed for two copper doped at Ti site (Ti22Cu2O48) as well as two oxygen vacancies along with Cu doping at Ti site (Ti22Cu2O46). Spin-spin interaction results have been analyzed to understand the possibility of ferromagnetism in the copper doped rutile TiO2. It has been found that copper doped system with adjacent oxygen vacancies gives ferromagnetic ordering.