Lattice-Driven Ruthenates

Abstract

Ruthenates have extended 4d-electron orbitals and comparable Coulomb, crystalline electric field, and spin-orbit interactions, as well as significant p-d orbital hybridization and spin-lattice coupling. The physical properties of ruthenates are highly susceptible to even slight lattice distortions; as a result, external magnetic field, pressure, electrical current, and chemical doping can generate disproportionate responses in structural as well as other physical properties, which can lead to unusual ground states or phenomena. Examples of the unusual, strong coupling of the ruthenates to external stimuli include negative volume thermal expansion via orbital and magnetic order in doped Ca2RuO4, colossal magnetoresistivity via avoiding a spin-polarized state and quantum oscillations in Ca3Ru2O7, and pressure-induced transition from ferromagnetism to antiferromagnetism in Sr4Ru3O10.