First-Principles Investigation On The Magnatic Properties And Electronic Structures And Phonon Instabilities Of The Tetragonal SrRuO₃

SrRuO3has three remarkable features. First, it is a moderately correlated material that exhibits several novel physical properties; second, it permits the epitaxial growth of essentially single-crystal films; and third, because it is a good conductor, it has attracted interest as a conducting layer in epitaxial heterostructures with a variety of functional oxides. In this paper, we investigate the evolution of magnetic properties of tetragonal SRO with the in-plane lattice constant α varying within the range3.70A～4.22A. The calculations reveal two critical lattice constants (α=3.85A and4.11A), at which the magnetic moment of Ru atom experiences an abrupt change. When3.85A <a<4.11A, the magnetic moment of Ru atom gradually increases with the increasing lattice constant α. Under the in-plane compressive strain with α～3.85A, a ferromagnetic to nonmagnetic transition is induced. When α～4.11A, magnetic moment of Ru atom sharply decreases to a small value. To distinguish these two ferromagnetic states, we call the one with larger magnetic moment strong ferromagnetic state, and the other weak ferromagnetic state. Detailed electronic structure analyses, together with the Stoner criterion are adopted to find the cause of these different magnetic states.Using density-functional theory calculations, we investigate the magnetic as well as the dynamical properties of tetragonal SrRuO3under the influence of epitaxial strain. It is found that both the tensile and compressive strain in the xy-plane could induce the abrupt change in the magnetic moment of Ru atom. In particular, under the in-plane～4%compressive strain, a ferromagnetic to nonmagnetic transition is induced. Whereas for the tensile strain larger than3%, Ru’s magnetic moment drops gradually with the increase of the strain, exhibiting a weak ferromagnetic state. We find that such magnetic transitions could be qualitatively explained by the Stoner model. In addition, frozen phonon calculations at Γ point and phonon dispersion calculation reveal structural instabilities could occur under both compressive and tensile strains. Such instabilities are very similar to those of the ferroelectric perovskite oxides, even though SRO remains to be metallic in the range we studied. These might have influence on the physical properties of oxide supercells taking SRO as constituent.