The Tanabe–Sugano diagrams, developed by Yukito Tanabe and Satoru Sugano in 1954, show how the energy levels of electrons in the d-orbitals split under the influence of a ligand field. These diagrams help reveal the details about optical responses, magnetic properties, and electronic behaviors of transition-metal complexes and compounds.

Commemorating 70 years of the Tanabe–Sugano diagrams, the Journal of the Physical Society of Japan has curated a special topics collection “70 Years of the Tanabe–Sugano Diagrams,” showcasing the latest advancements in the research field inspired by these diagrams and ligand field theory.

Norimichi Kojima explores the dynamical changes of spin configuration in iron-based complexes, which are predicted by the Tanabe–Sugano diagrams and crucial for developing advanced magnetic materials.

Atsushi Fujimori uses the ligand field theory with another approach called configuration interaction theory to describe the electronic properties of various transition-metal compounds and complexes.

Naoya Iwahara explores the dynamic Jahn-Teller effect in heavy transition-metal compounds, specifically in cubic 4d- and 5d- systems, and its impact on their electronic and magnetic properties.

Masahito Mochizuki examines multiferroics, or materials in which magnetism and ferroelectricity coexist. It highlights the discovery of perovskite manganese oxide, where magnetic order induces ferroelectricity, creating strong magnetoelectric coupling.

Akihiko Ikeda and colleagues explore the unique spin crossover behavior and new magnetic phases in lanthanum cobaltite using state-of-the-art high-magnetic field generating systems.

Ashish Chainani and colleagues applied the principles of ligand field theory to study rare earth-transition-metal ferrimagnets using advanced X-ray spectroscopy techniques.

Robert Green and George A. Sawatzky investigate the variations in energy levels of transition-metal compounds, focusing on the role of ligand holes.

The studies in this special collection underscore the continued relevance of the Tanabe–Sugano diagrams for developing materials with superior optical, magnetic, and catalytic properties for advanced applications.

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