Mg-doping enhanced superconductivity and ferromagnetism in Ti1− xMgxO films

Abstract The structure, electrical transport, and magnetic properties have been systematically studied in superconducting Ti1−xMgxO (x = 0, 0.003, 0.02, 0.08, and 0.27) films. It is found that, both the zero resistance and onset superconducting transition temperatures of Ti1−xMgxO first increase with increasing the Mg content from x = 0 to x = 0.02, and then decrease with the further increase of x. More interestingly, the Mg-doping simultaneously introduces a ferromagnetic order into this superconducting system, and the ferromagnetism gradually increases with increasing Mg content. According to the first-principles calculations, the non-monotonous Mg doping-dependent superconductivity, carrier density, and disorder strength may be explained as that the Mg atoms first fill the Ti vacancy sites and then substitute the Ti atoms. The calculations also reveal that the ferromagnetism is highly related to the spin polarization of 3d states of Ti atoms surrounding Mg atoms. The discovery of enhanced superconductivity with coexisting ferromagnetism in Ti1−xMgxO films provides an excellent platform to investigate the interaction between superconductivity and ferromagnetism.