ELFT HÍRADÓ

[Szeminárium koordinátor <sem-admin AT szfki.hu>]

SZFI SeminarStefan BlügelPeter Grünberg Institute and Institute for Advanced 
Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany (host: Rózsa 
Levente)Spin Models for Modeling MagnetsMonday, 6 November 2023, 10:00, KFKI 
Campus, Bldg. 1, 2nd floor, Conference RoomIt has become common practice to 
study the stability, dynamics, thermodynamics and phase diagrams of magnets 
using classical spin-lattice models with pairwise exchange interactions of 
the Heisenberg type. In recent years, however, the focus has been on 
increasingly complex magnetic structures, including noncollinear spin 
textures such as skyrmions, many of which arise from a competition of 
different spin interactions. On the other hand, we studied magnets with 
increasingly involved and complex electronic structures. As a consequence, we 
witnessed additional interactions that had to be added to the established 
spin-models more and more often to explain the magnetic order 
(four-spin-three-site interaction [1,2], four-spin-four-site interaction [3], 
chiral-biquadratic interaction [4-7], topological chiral-chiral and 
spin-chiral interaction [8], etc.). This sounds like a very spontaneous, 
unsatisfactory case-by-case procedure, and it seems totally unclear whether 
all important interactions are captured or important ones are still missing. 
In this lecture, I present an attempt to derive systematically the spin 
Hamiltonian of all exchange interactions from the very general principle of 
indistinguishability of electrons in a many-electron system. This provides 
arguably a rigorous ansatz for reasonable spin-Hamiltonians.Work was carried 
out in collaboration with Hiroshi Katsumoto, Fabian Lux and Yuriy 
Mokrousov.Funding from Deutsche Forschungsgemeinschaft (DFG) through SPP-2137 
(project BL444/16-2) and SFB-1238 (project C01) is greatly acknowledged.[1] 
M. Hoffmann, S. Blügel, PRB 10, 024418 (2019).[2] A. Krönlein, M. Schmitt, M. 
Hoffmann, J. Kemmer, N. Seubert, M. Vogt, J. Küspert, M. Böhme, B. Alonazi, 
J.Kügel, H. A. Albrithen, M. Bode, G. Bihlmayer, and S. Blügel, PRL 120, 
207202 (2018).[3] D. J. Thouless, Proc. Phys. Soc. 86, 893 (1965).[4] A. 
Lászlóffy, L. Rósa, K. Palotás, L. Udvardi, and L. Szunyogh, Phys. Rev. B 99, 
184430 (2019).[5] S. Brinker, M. d. S. Dias, and S. Lounis, New Journal of 
Physics 21, 083015 (2019).[6] S. Mankovsky, S. Polesya, and H. Ebert, Phys. 
Rev. B 101, 174401 (2020).[7] M. dos Santos Dias, S. Brinker, A. Lászlóffy, 
B. Ny ́ ari, S. Blügel, L. Szunyogh, and S. Lounis, Phys. Rev. B103, L140408 
(2021).[8] S. Grytsiuk, J.-P. Hanke, M. Hoffmann, J. Bouaziz, O. Gomonay, G. 
Bihlmayer, S. Lounis, Y. Mokrousov, S.Blügel, Nat. Commun. 11, 511 
(2020). Minden érdeklődőt szívesen látunk! - Everyone is welcome to 
attend.Attila Nagysem-admin AT szfki.hu