Micromagnetics is the continuous theory of magnetization distributions that describes both statics and dynamics. The theory was developed progressively from 1932, and it was formalized by William F. Brown in his book Micromagnetics (1963). Work was initially purely analytic, but numerical micromagnetics appeared soon after (A.E. LaBonte, 1969). Our group is involved in both aspects of micromagnetics. Today, several numerical micromagnetic open codes exist to which we contribute (OOMMF, MuMax3).

In our group, pioneering works were performed by Jacques Miltat, since 1984, in the framework of finite differences. It was initially two-dimensional (a cross-section of an infinite thin film), and the dipolar energy was calculated by direct summation, with a calculation cost growing as N*N, N being the number of cells. In the 90’s, fast Fourier transforms (FFT) were introduced to replace direct summation, decreasing the calculation cost to N log(N). Together with the increase of computer capacities (RAM, FLOPS), this allowed treating three-dimensional problems.

In 2010, the code was completely rewritten so as to run on a GPU, keeping its high accuracy as all calculations are performed with double precision. Although the code is not as optimized as the open codes quoted above, and therefore is slower and can handle fewer cells, it offers several advantages:

  • it is immediate to add a new energy term; this was very important in 2012 when the interfacial Dzyaloshinskii-Moriya interaction (DMI) started to be considered, as well as in 2004 when spin-transfer torque (STT) was invented.
  • it is simple to prepare derived codes, such as an atomic micromagnetic model as required for very small structures, or a multi-space nudged elastic band technique to compute micromagnetic energy barriers, or a 2D code solving the Slonczewski equations for the dynamics of a general domain wall in a bubble garnet film.
  • it gives confidence in modifying the open codes, like the DMI routine added to OOMMF.

Recently, our numerical works has most been performed using MuMax3, which enables fast simulations on large area. A particular effort has been devoted to implement on this platform calculations for antiferromagnets, ferrimagnets and recently on disordered samples.

Recent publications

  • Spin-orbit torque driven domain wall motion in the absence of Dzyaloshinskii-Moriya interactions

A. Thiaville, J. Miltat, Europhys. Lett.  146, 66001(7) (2024).

  • Reversal of the skyrmion topological deflection across ferrimagnetic angular momentum compensation

L. Berges, R. Weil, A. Mougin, J. Sampaio, Appl. Phys. Lett. 123, 142404(6) (2023).

  • Skyrmion inertia in synthetic antiferromagnets

S. Panigrahy, S. Mallick, J. Sampaio, S. Rohart, Phys. Rev. B 106, 144405(8) (2022).

  • Size-dependent mobility of skyrmions beyond pinning in ferrimagnetic GdCo thin films

L. Berges, E. Haltz, S. Panigrahy, S. Mallick, R. Weil, S. Rohart, A. Mougin, J. Sampaio, Phys. Rev. B 106, 144408(10) (2022).

  • Domain wall dynamics in antiferromagnetically coupled double-lattice systems

Eloi Haltz, Sachin Krishnia, Léo Berges, Alexandra Mougin, and João Sampaio, Phys. Rev. B 103, 014444(15) (2021).

  • Chiral magnetic domain walls under transverse fields: a semi-analytical model

P. Géhanne, A. Thiaville, S. Rohart, V. Jeudy, J. Magn. Magn. Mater. 530, 167916(11) (2021).

  • Domain wall propagation by spin-orbit torques in in-plane magnetized systems

R. Kohno, J. Sampaio, S. Rohart, A. Thiaville, Phys. Rev. B 102, 020410(5) (2020).

  • Study of the velocity plateau of Dzyaloshinskii domain walls

V. Krizakova,  J. Peña Garcia, J. Vogel, N. Rougemaille, D. de Souza Chaves, S. Pizzini, A. Thiaville, Phys. Rev. B 100, 214404(9) (2019).