Field-induced half-metallic phase in epitaxial TcO2 bilayer on rutile TiO2 surface

For spintronic applications, it is highly desirable to realize 100%-spin-polarized two-dimensional (2D) electron systems in field-controllable epitaxial ultrathin films or 2D materials on semiconductor substrates. Through systematic first-principles investigation, we find that one epitaxial TcO 2 bilayer on rutile TiO 2 (001) substrate is an antiferromagnet-like narrow-gap semiconductor, and its electronic and magnetic properties can be manipulated through electric field. When electric field reaches 0.03 V/A, it transits to a half-metallic ferrimagnet with 100% spin polarization. Our analysis indicates that in both phases the magnetization density and the electronic states near the Fermi level originate mainly from the TcO 2 bilayer, and across the interface the bond lengths and angles quickly converge to the corresponding values of the bulk TiO 2 . Therefore, the heterostructure actually hosts a 2D electron system determined by the TcO 2 bilayer and the TiO 2 substrate. Because the half-metallic phase can be achieved from a nonmetallic phase, such epitaxial 2D electron systems should be usable in spintronic devices.