Ferromagnetic insulators are uncommon

Magnetic interactions in oxides have been extensively studied by John B. Goodenough, one of the three recipients of the 2019 Nobel Prize in Chemistry. His models of direct and indirect exchange interactions form part of the foundation of our own R&D, as demonstrated in our recent publication in Annalen der Physik.

As noted by P. W. Anderson in his classic paper New approach to the theory of superexchange interactions, Phys. Rev. 115, 2–13 (1959), the dominant coupling between magnetic cations in most compounds is antiferromagnetic—even in many ferrimagnetic materials. This is why true ferromagnetic insulators are rare, and room‑temperature ferromagnetic insulators are exceptionally uncommon. As a result, experiments requiring insulating ferromagnets are typically carried out at cryogenic temperatures using specialized, high‑cost instrumentation.

The impact of room‑temperature insulating ferromagnets on practical devices is significant

The importance of understanding magnetic and disordered systems was recognized by the 1977 Nobel Prize in Physics, awarded to Philip W. Anderson, Sir Nevill F. Mott, and John H. van Vleck for their fundamental theoretical contributions. Their work underpins much of today’s research into magnetic materials and continues to guide the development of new device concepts.