Symmetry‐Mismatch‐Induced Ferromagnetism in the Interfacial Layers of CaRuO₃/SrTiO₃ Superlattices

Abstract

By modifying the entangled multi‐degrees of freedom of transition‐metal oxides, interlayer coupling usually produces interfacial phases with unusual functionalities. Herein, a symmetry‐mismatch‐driven interfacial phase transition from paramagnetic to ferromagnetic state is reported. By constructing superlattices using CaRuO3 and SrTiO3, two oxides with different oxygen octahedron networks, the tilting/rotation of oxygen octahedra near interface is tuned dramatically, causing an angle increase from ≈150° to ≈165° for the RuORu bond. This in turn drives the interfacial layer of CaRuO3, ≈3 unit cells in thickness, from paramagnetic into ferromagnetic state. The ferromagnetic order is robust, showing the highest Curie temperature of ≈120 K and the largest saturation magnetization of ≈0.7 µB per formula unit. Density functional theory calculations show that the reduced tilting/rotation of RuO6 octahedra favors an itinerant ferromagnetic ground state. This work demonstrates an effective phase tuning by coupled octahedral rotations, offering a new approach to explore emergent materials with desired functionalities.

Charge-Transfer-Induced Interfacial Ferromagnetism in Ferromagnet-Free Oxide Heterostructures

“…CRO is an orthorhombically structured PM metal, showing non-Fermi-liquid behavior at low temperatures. 22 In comparison with its sister system, the itinerant ferromagnet SrRuO 3 (SRO), CRO has a larger orthorhombic distortion, which causes the degeneracy of t 2g band and a relatively low density of states N(E F ) near the Fermi surface. 23,24 As a result, CRO remains PM down to 2 K in either bulk or thin film forms.…”

“…In this paper, we pay attention to a special superlattice (SL) formed by two typical PM oxides: the 4d ruthenate CRO and 3d nickelate LNO. CRO is an orthorhombically structured PM metal, showing non-Fermi-liquid behavior at low temperatures . In comparison with its sister system, the itinerant ferromagnet SrRuO 3 (SRO), CRO has a larger orthorhombic distortion, which causes the degeneracy of t 2g band and a relatively low density of states N ( E F ) near the Fermi surface. , As a result, CRO remains PM down to 2 K in either bulk or thin film forms. , Different from CRO, LNO is rhombohedrally structured.…”