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Ferromagnetic insulators are unusual

Magnetic interactions in oxides were intensively studied by John B. Goodenough, one of three winners of the Nobel Prize in Chemistry 2019. His models explaining the direct and indirect interactions were applied in our R&D, examples of which are given in our recent paper published in the Annalen der Physik-journal. As was pointed out by P. W. Anderson in New approach to the theory of superexchange interactions. Phys. Rev. 115, 2-13 (1959), the prevailing coupling between magnetic cations in most of the compounds is antiferromagnetic, which includes also ferrimagnetic materials. This counts for the fact that ferromagnetic insulators are rare compounds, yet those operating at room-temperature are indeed unique. Correspondingly, experiments and characterizations requiring genuine insulating ferromagnets are conducted at cryogenic temperatures, thus requiring expensive techniques characteristic to well-equipped research laboratories.

 

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

The Nobel Prize in Physics 1977 was awarded jointly to Philip Warren Anderson, Sir Nevill Francis Mott and John Hasbrouck van Vleck "for their fundamental theoretical investigations of the electronic structure of magnetic and disordered systems".