Non-magnetic impurity induced magnetism in rutile TiO2:K compounds

Recent ab initio studies have theoretically predicted room temperature ferromagnetism in several oxide materials of the type AO(2) in which the cation A(4+) is substituted by a non-magnetic element of the 1 A column. Our purpose is to address experimentally the possibility of magnetism in Ti1-xKxO2 compounds. The samples have been synthesized via the solid state route method at equilibrium. Our study has shown that Ti1-xKxO2 is thermodynamically unstable and leads to a phase separation, in contradiction with the hypothesis of ab initio calculations. In particular, the crystalline TiO2 grains appear to be surrounded by K-based phase. The oxidization state of the Ti ion is found to be in Ti4+ as confirmed from the x-ray photoelectron spectra measurement. Nevertheless, K: TiO2 compounds exhibit weak paramagnetism with the highest magnetic moment of similar to 0.5 mu(B) K-1 but no long-range ferromagnetic order. The observed moment in these compounds remains much smaller than the predicted moment of 3 mu(B) by ab initio calculation. The apparent contradictions between our experiments and first-principles studies are discussed.