Domain Wall Motion In Nanostrips Research Articles

Spin-wave resonance reflection and spin-wave induced domain wall displacement

Spin-wave propagation and spin-wave induced domain wall motion in nanostrips with a Néel wall are studied by micromagnetic simulations. It is found that the reflection of spin waves by the wall can be resonantly excited due to the interaction between spin waves and domain-wall normal modes. With the decrease of the saturation magnetization Ms (and the consequent increase of the wall width), the reflection is diminished and complete transmission can occur. The domain wall motion induced by spin waves is closely related to the spin-wave reflectivity of the wall, and may exhibit different types of behavior. The reflected spin waves (or magnons) give rise to a magnonic linear momentum-transfer torque, which drives the wall to move along the spin wave propagation direction. The maximal velocity of the domain wall motion corresponds to the resonance reflection of the spin waves. The transmitted spin waves (or magnons) lead to a magnonic spin-transfer torque, which drags the wall to move backwardly. The complicated domain wall motion can be described qualitatively by a one-dimensional model incorporating both the magnonic linear momentum-transfer torque and the magnonic spin-transfer torque. The results obtained here may find use in designing magnonic nanodevices.

Current induced domain wall motion in nanostripes with perpendicular magnetic anisotropy

We report micromagnetic modeling results of current induced domain wall (DW) motion in magnetic devices with perpendicular magnetic anisotropy by solving the Landau–Lifschitz–Gilbert equation including adiabatic and non-adiabatic terms. A nanostripe model system with dimensions of 500 nm ( L)×25 nm ( W)×5 nm ( H) was selected for calculating the DW motion and its width, as a function of various parameters such as non-adiabatic contribution, anisotropy constant ( K u ), saturation magnetization ( M s ), and temperature ( T). The DW velocity was found to increase when the values of K u and T were increased and the M s value decreased. In addition, a reduction of the domain wall width could be achieved by increasing K u and lowering M s values regardless of the non-adiabatic constant value.

Intrinsic Threshold Current Density of Domain Wall Motion in Nanostrips With Perpendicular Magnetic Anisotropy for Use in Low-Write-Current MRAMs

In this paper, we have calculated the intrinsic threshold current density of domain wall (DW) motion in nanostrips with perpendicular magnetic anisotropy (PMA) and have estimated writing properties of magnetic random access memories (MRAMs) with DW motion. Carrying out a micromagnetic simulation, we revealed that the intrinsic threshold current density decreases with decreases in the strip thickness, width, and magnetization, whereas it did not depend significantly on magnetocrystalline anisotropy and exchange stiffness. These results showed good agreement with one-dimensional (1-D) analysis. We also found that current-induced DW motion in PMA strips may have potential for use in low-write-current MRAMs. For a width of less than roughly 100 nm, comparable properties to those of existing memories can be obtained.

Fast domain wall motion in nanostripes with out-of-plane fields

Controlling domain wall motion is important due to the impact on the viability of proposed nanowire devices. One hurdle is slow domain wall speed when driven by fields greater than the Walker field due to nucleation of vortices in the wall. We present simulation results detailing the dynamics of these vortices including the nucleation and subsequent fast ejection of the vortex core leading to fast domain wall speeds. The ejection is due to the reversal of the core moments by an out-of-plane field. The technique can be used to produce domain walls of known orientation, independent of the initial state.

Micromagnetic analysis of current driven domain wall motion in nanostrips with perpendicular magnetic anisotropy

Current driven domain wall motion in nanostrips with perpendicular magnetic anisotropy was analyzed by using micromagnetic simulation. The threshold current density of perpendicular anisotropy strips in adiabatic approximation was much smaller than that of in-plane anisotropy strips, and it reduced with thickness reduction. The differences originate from the differences in domain wall width and hard-axis anisotropy. Also, the threshold current density of perpendicular anisotropy strips required to depin from a pinning site was quite small although the threshold field of the strips was sufficiently large relative to those of in-plane anisotropy strips.