Research project: Computational benchmarks for micromagnetic simulations

In the micromagnetic community, the National Institute of Standards and Technology has initiated the collection of such micromagnetic standard problems [1], and made 4 such problems together with solutions from a variety of groups and codes available.

The Southampton micromagnetic modelling group has developed and contributed two more problems that address (i) micromagnetic systems driven with a spin-polarised current, and (ii) studies of dispersion relations as done in the emerging field of magnonics.

(i) the combination of conventional micromagnetics with the Zhang-Li Spin-torque transfer term is studied [2] for a well defined problem using OOMMF, M3S, Nmag and analytical methods, with partners fromt the University of Hamburg (Germany) and IBM Zuerich (Switzerland). We propose to a standard problem system to be a permalloy cuboid of 100 nm edge length in x and y direction,and 10 nm thickness, which contains a Landau pattern with a vortex in the center of the structure. A spin-polarized dc current density of 10^12 A/m^2 flows laterally through the cuboid and moves the vortex core to a new steady-state position. We show that the new vortex-core position is a sensitive measure for the correctness of micromagnetic simulators that include the spin-transfer torque. We compute, show and compare numerical results from four different finite-difference and finite-element-based simulation tools. We also show the solution of an approximate but analytical model. Simulation scripts are available for download [3].

(ii) The spin wave dispersion in a magnonic waveguide is studied with partners from India and Poland. Dispersion relations are important to design the next generation of signal processing logic based on low-energy magnetic information carrier technology, and increasingly researchers in academia and industry use micromagnetic packages to compute those. This publication [4] details how the dispersion relation can be extracted from conventional micromagnetic dynamics simulations, and provides a particular example that can be used to validate against.



[1] http://www.ctcms.nist.gov/~rdm/toc.html#standards

[2] http://link.aip.org/link/?JAPIAU/105/113914/1  

[3] https://www.southampton.ac.uk/~fangohr/publications/2009-proposal-for-a-standard-problem-for-micromagnetic-simulations-including-spin-transfer-torque/index.html
 
[4] http://dx.doi.org/10.1109/TMAG.2012.2206820