Effects of atomic displacements on band gaps of Na2MgXO6 (X= Co, Fe) double perovskite oxides: GGA and GGA+U approaches

Abstract

True half-metallic materials are among the most preferred material groups in spintronic applications with their 100% spin polarization. Perovskite materials have formed the basis of many semiconductor devices in recent years with their widespread technological use. In this study, Na2MgXO6 (X = Co, Fe) perovskite oxides were obtained as true half-metallic materials, and the effects of the atomic displacements between Mg and Co/Fe atoms on electronic, magnetic and half-metallic characters were investigated. First, volume-energy optimization curves were calculated, and ferromagnetic phases were energetically more stable. Second, electronic calculations were performed, and semiconducting band gaps were seen in the up-spin states. The band gaps of Na2MgCoO6 and Na2CoMgO6 oxides were obtained as 0.531 eV and 1.1446 eV, respectively. Then atomic displacements between Mg and Co/Fe-transition metals happened and band gaps of Na2MgFeO6 and Na2FeMgO6 oxides were obtained as 0.487 eV and 2.142 eV, respectively. As can be seen, the atomic structure changes directly affected the band gaps. Additionally, GGA + U interactions were performed for electronic calculations. As a result of increasing U-interactions, band gaps decreased. It is possible to say that all band gaps change with the effect of atomic compositions. Finally, the total magnetic moments of Na2MgCoO6 and Na2MgFeO6 oxides were obtained as 5.00 μB/f.u. and 6.00 μB/f.u., respectively. Na2MgXO6 (X = Co, Fe) oxides with half-metallic ferromagnetic features and high magnetic moment values are very useful materials for spintronic applications.