Field-induced half-metallic phase in epitaxial TcO[formula omitted] bilayer on rutile TiO[formula omitted] surface

Abstract

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 TcO2 bilayer on rutile TiO2 (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/Å, 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 TcO2 bilayer, and across the interface the bond lengths and angles quickly converge to the corresponding values of the bulk TiO2. Therefore, the heterostructure actually hosts a 2D electron system determined by the TcO2 bilayer and the TiO2 substrate. Because the half-metallic phase can be achieved from a nonmetallic phase, such epitaxial 2D electron systems should be usable in spintronic devices.