On **December 20th at 11:00**, we have the pleasure to welcome** Dr. Yaroslav Kvashnin** from Uppsala University who will give a seminar at CEA/SPINTEC, Bat 1005, room 445, entitled :

**Magnetic interactions and excitations from first principles**

Magnetization dynamics on the nanoscale can be well described by Landau-Lifshitz(-Gilbert) equation of motion. If properly parameterized, it enables to model magnon excitations and finite-temperature magnetic properties of real materials. Here a common practice is to assume that the atomistic magnetic moments interact with each other via Heisenberg exchange coupling (J) (see e.g. [1]).

The basic mechanisms which give rise to the exchange coupling are quite well-known [2]. However, when it comes to real materials, predicting the sign and the magnitude of exchange parameters is an extremely challenging problem. There are difficulties related with itinerant character of magnetism, importance of correlation effects and in general competition between various exchange mechanisms (see e.g. [3]).

In this talk I will give an overview of the methods which allow us to calculate the exchange interactions from first principles electronic structure. One of them is based on the analysis of the DFT total energies [4] and the other one is a linear-reponse-type approach [5]. I will show that the two methods give different results even in the case of insulating transition metal oxides, where the magnetic moments are well localized and the magnetic interactions are of super-exchange nature. I will argue that these differences originate from the spin-polarization of the exchange-correlation functional, which can in general be circumvented [6].

References:

[1] O. Eriksson et al, “Atomistic Spin Dynamics: Foundations and Applications” (Oxford University Press, 2017)

[2] P. Fazekas, Lecture Notes on Electron Correlation and Magnetism (1999)

[3] YK et al, Phys. Rev. Lett. 116, 217202 (2016)

[4] Xiang, H., Lee, C., Kooc, H.-J., Gong, X. & Whangbo, M.-H, Dalton Trans. 42, 823–853 (2013)

[5] A. I. Liechtenstein et al., J. Magn. Magn. Mater., 67, 65 (1987) ; M.I. Katsnelson and A.I. Lichtenstein, Phys. Rev. B 61 8906 (2000)

[6] S. Keshavarz, J. Schött, A. J. Millis, and YK, Phys. Rev. B 97, 184404 (2018)

(*) Persons who do not have a CEA badge must request an entry authorization sufficiently in advance, not later than Thursday December 12th at mair.chshiev@cea.fr or celine.conche@cea.fr