Properties of single RuO₂ layer embedded in SrTiO₃

A two-dimensional ferromagnet is an interesting system both for basic understanding of magnetism and for spintronic applications. However, making such a system is not easy as ferromagnetism becomes more and more unstable with reducing the thickness of a ferromagnet. For example, in oxide systems such as SrRuO₃, La_1-xSr_xMnO₃, etc, ferromagnetism is lost around the thickness of a few unit cells [1, 2]. Recent theoretical studies have shown that a single SrRuO₃ layer can exhibit half-metallicity when it is sandwiched between SrTiO₃ lattices [3, 4]. The conduction electrons are predicted to exist only in RuO₂ layers, which means that the system is a two-dimensional half-metal. In this work, in order to demonstrate the theoretical prediction, we have fabricated high-quality SrRuO₃/SrTiO₃ superlattices using molecular beam epitaxy. Magnetic and transport measurements show a clear signature of ferromagnetism and conductivity.