#### Date

December 1, 2015 14:00 – 15:30

#### Venue

TOKYO ELECTRON House of Creativity 3F, Lecture Theater, Katahira Campus, Tohoku University

【MAP】

#### Speakers

Thierry Valet (SPICE Center, Johannes Gutenberg University, Mainz, Germany)

Helen Gomonay (SPICE Center, Johannes Gutenberg University, Mainz, Germany)

#### Title and Abstract

14:00 –

**Thierry Valet (SPICE Center, Johannes Gutenberg University, Mainz, Germany)**

Title:

Spectral Methods for Micro-magnetic Simulations

Abstract:

Several physical properties of major current interest for magnetic nano-devices are determined by the small amplitude magnetization dynamics within a finite bandwidth, in the vicinity of an extremum of the micro-magnetic energy functional. Among the most salient examples in this class of problem we shall mention: spin wave band structures in magnonic crystals, (linear) resonance spectra (FMR, MRFM, spin diodes c), thermal magnetization fluctuations (magnoise) around a stationary state, and the onset of the dynamic instability under spin transfer or spin orbit torque. In such cases one can safely linearize the magnetization equation of motion around the considered equilibria. The resulting linear dynamic equations can be further cast into an eigenvalue (spectral) problem, for a strictly differential linear operator, after Fourier transform in the time variable and introduction of a magneto static potential. We will discuss how this is then amenable to extremely efficient finite element numerical implementations, taking advantage of state of the art linear algebra libraries. Numerical results for various physical examples will be presented and discussed, illustrating the versatility and power of this approach. In some cases orders of magnitude improvements in computational time are achieved compared to more traditional approaches (time domain solution of the nonlinear LLG equations + FFT in time). If time allows, the relevance of spectral calculations in the context of some fully non-linear problems will be also outlined (amplitude equations, string methods c).

14:45 –

**Helen Gomonay (SPICE Center, Johannes Gutenberg University, Mainz, Germany)**

Title:

Berry-phase effects in noncollinear antiferromagnets

Abstract:

Antiferromagnets are promising materials for spintronic applications as they are faster and more energy-saving as their ferromagnetic counterpart. An important problem of AFM spintronics is the coupled dynamics of free carriers and localized magnetic moments. In my talk I consider the adiabatic dynamics of spin-polarized electrons in a metallic AFM exhibiting a noncollinear 120 magnetic structure. The slowly varying AFM spin texture produces a non-Abelian gauge potential related to the time and space gradients of the N L eel vectors. Corresponding emergent electric and magnetic fields induce rotation of spin and influence the orbital dynamics of free electrons. I discuss both the possibility of a topological spin Hall effect in the vicinity of topological AFM solitons with nonzero curvature and rotation of the electron spin traveling through the AFM domain wall.effect of antiferromagnetic texture on the motion of free electron.