Hillert Materials Modeling Colloquium series XVIII: Quantitative theory of magnetic interactions in solids

Magnetic ordering and related phenomena are of essentially quantum and essentially many-body origin and require strong enough electron-electron interactions. Also, they are very sensitive to the details of electronic structure of specific materials. This makes a truly microscopic description of exchange interactions a challenging task. Long ago we suggested a general scheme of calculations of exchange interactions responsible for magnetism based on the “magnetic force theorem”. It was formulated originally as a method to map the spin-density functional to effective classical Heisenberg model, the exchange parameters turned out to be, in general, essentially dependent on initial magnetic configuration and not universal. However, they are directly related to the spin-wave spectrum and, thus, can be verified experimentally. This approach also lies in the base of “ab initio spin dynamics” within the density functional approach.

It is well known now that this scheme is, in general, insufficient for strongly correlated systems and should be combined with the mapping to the multiband Hubbard model and use of, say, dynamical mean-field theory (DMFT) to treat the latter. Our original approach can be reformulated within the DMFT. The method can be also modified to calculate Dzialoshinskii-Moriya interactions which play a crucial role in the phenomenon of weak ferromagnetism, in physics of magnetic skyrmions, and in magnonics/spintronics in general. I will discuss both general methods and their applications to electronic structure and magnetism of various groups of magnetic materials including elemental transition and rare-earth metals, half-metallic ferromagnets, transition metal oxides, molecular magnets, sp electron magnets, and novel two-dimensional magnetic materials.

Reference: A. Szilva, Y. Kvashnin, E. A. Stepanov, L. Nordström, O. Eriksson, A. I. Lichtenstein, and M. I. Katsnelson, Rev. Mod. Phys. 95, 35004 (2023)

Lecturer

Professor Mikhail Katsnelson was born in 1957 in Magnitogorsk, an industrial city in Southern Ural (USSR). After studying theoretical physics in Ural State University he was working in the Institute of Metal Physics in Ekaterinburg. From 2004 he is professor of theory of condensed matter at Radboud University, Nijmegen (Netherlands). Main works are on physics of two-dimensional materials, magnetism, and strongly correlated systems. Awarded by several prizes for his scientific achievements, including Spinoza Prize and Hamburg Prize for Theoretical Physics. He is elected member of Royal Netherlands Academy of Arts and Sciences, Academia Europaea, Uppsala Royal Scientific Society, and honorary doctor of Uppsala University.

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