Investigations of domain-wall motion using atomistic spin dynamics
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
In this thesis, current driven domain-wall motion is studied using atomistic simulations with the exchange coupling modeled by the Heisenberg Hamiltonian under the nearest-neighbor approximation. The investigations may be divided into two parts, each concerned with how different aspects of the systems affect the domain-wall motion. The first part deals with domain-wall width dependence of the velocity in a three dimensional geometry with simple cubic crystal structure and uniaxial anisotropy. Results from this part showed that the velocity has a minor domain-wall width dependence. For a fixed current density, the velocity increased with domain-wall width, though only from 61.5 a/ns to 64.5 a/ns as the domain-wall width was increased from 3 to 25 atoms.
The second part of the investigations deals with phenomena involving mixed cubic and uniaxial anisotropy, the non-adiabaticity parameter as well as the geometry of the system. The discussion includes an account of how the spin-transfer and cubic anisotropy torques contribute to the motion for different values of the non-adiabaticity parameter. In comparing a one dimensional atomic chain and a three dimensional system with simple cubic crystal structure, but otherwise with the same material properties, results showed a difference in how the two systems responded to currents. This difference is not accounted for by the micromagnetic theory, and its origin was unable to be determined.
Place, publisher, year, edition, pages
2015. , 54 p.
UPTEC F, ISSN 1401-5757 ; 15010
spin-transfer torques, non-adiabaticity, Walker breakdown, atomistic simulations
IdentifiersURN: urn:nbn:se:uu:diva-247556OAI: oai:DiVA.org:uu-247556DiVA: diva2:796867
Master Programme in Engineering Physics
Nyberg, TomasPereiro, Manuel