# Proposal for a Standard Micromagnetic Problem: Spin Wave Dispersion in a Magnonic Waveguide¶

G. Venkat, D. Kumar, M. Franchin, O. Dmytriiev, M. Mruczkiewicz, H. Fangohr, A. Barman, M. Krawczyk and A. Prabhakar

online: journal, local preprint pdf (SW_standard_problem_Pre_print.pdf)

## Motivation¶

- The micromagnetic standard problems (www.ctcms.nist.gov/~rdm/stdplan.html) allow to compare the simulation results of different simulation tools and help finding bugs and errors.
- Here we propose a new standard problem that computes spin wave dispersion of a permalloy stripe using different micromagnetic packages

## Summary¶

- We propose a standard micromagnetic problem which involves a nanostripe of permalloy
- The magnetization dynamics is studied and methods to extract features from simulations are described. The image below shows spin waves propagating as a function space and time.

- Spin wave dispersion curves, relating frequency and wave vector, are obtained for wave propagation in different configurations
- Simulation results obtained using both finite element (Nmag) and finite difference (OOMMF) packages are compared against analytic results

## Selected results¶

The dispersion curves compared against the analytic equations (dotted lines).

## Supporting material¶

**Prerequisites : It is assumed that netgen, nmag, numpy and matplotlib are installed in and defined in the PATH of the linux system.**

**The Nmag mesh**- The mesh file (nanowire.nmesh.h5) is generated using the open source meshing utility Netgen using the included geometry file (geom_1000.geo)**The Nmag simulation script**- The simulation script (run.py) has details of the simulation. The comments in it should be self explanatory. Notice that it uses the HLib library for compressing the BEM matrix generated during the simulation**The Nmag post processing script**- The post processing script (post_process.py) generates the spin wave space-time and dispersion plots from the simulation data. It is assumed that Numpy and matplotlib are both available.**The Makefile for the Nmag simulation**- This Makefile should run the entire simulation and then generate the dispersion curves. We strongly suggest this sort of approach because it reduces manual effort and the chances of errors.

**All the above files are included in the file stripe_simulation.zip**

**The OOMMF simulation scripts**- The relaxation script (OOMMF_static.mif) and the dynamics script (OOMMF_dynamics.mif) should help in setting up an OOMMF simulation to obtain dispersion curves.