Invited
Spin ordering regulation in room temperature multiferroic double perovskite oxides

Ferromagnetic spin ordering (neither ferrimagnetic nor canted antiferromagnetic) in multiferroic double perovskite oxides with Curie temperature above room temperature is strikingly persued. In this talk, I will present how to get this goal through paradigm-shifting and disruptive knowledge against the prevailing contraindicated perceptions on magnetism, ferroelectricity and insulating of perovskite oxides.

From viewpoint of emergentism, chemically intuitive and physically meaningful ensemble descriptors were constructed within framework of quantum mechanics and demonstrated feasible to predict perovskite oxides. Through mining out of reliable extant data of perovskite oxides, it was unveiled that ferroelectricity, spin ordering and electronic bandgap are predominantly controlled by the dynamic electronegativity of valence electrons, the configuration of magnetic cation dimers and the filling number of inner d subshell orbitals of B-site transition metal cations, respectively.

In double perovskite oxides composed of 3d5-3d3 cation on B-site in rocksalt-type configuration, the sign of net superexchange interaction was realized closely dependent on bond angle caused by octahedral distortion, which spans from negative to positive resulting from competition between ferromagnetic and antiferromagnetic superexchange interactions. A volcano-shaped trend between Weiss temperature Θ and 𝜇 × 𝑟𝐴/𝑟𝐵 (μ, rA and rB is reduced mass of primitive cell, A-site cation radius and B-site cation radius, respectively) ensemble descriptor was illustrated and able to quantitatively predict chemical composition of double-perovskite oxide for various spin ordering including ferromagnetism, spin frustration and ferrimagnetism. Curie temperature TC(FM) > 450K, a direct bandgap with ~ 0.8-1.7 eV at room temperature and negative temperature coefficient of resistivity in a range of 40-150oC were also determined experimentally.