Magnetization Reversal In Nanowires Research Articles

Magnetization reversal in nanowires with a spiral shape

Magnetic nanowires have been shaped in the form of spirals and arranged in different patterns. A two-dimensional periodic array of Fe spiral structures was fabricated by electron-beam lithography. The spirals had a radius of 2.8 μm, a linewidth of 100 nm, and a thickness of 20 nm. The magnetization reversal was studied by longitudinal vector magneto-optic Kerr effect (MOKE) in specular geometry as well as in Bragg MOKE geometry, using the diffraction spots from the grating for hysteresis measurements. The measurements are compared with the results of micromagnetic simulation, which allows a detailed interpretation of the experimental data. The magnetization reversal is characterized by an onion state in remanence and a coercivity which is different for the inner and outer parts of the spiral structures. In general the inner parts of the spiral are more stable and switch later than the outer ones. The switching of the outer parts depends on the boundary condition.

Domain wall structure transition during magnetization reversal process in magnetic nanowires

The analytical micromagnetics and numerical simulations were used to investigate the domain wall structure during the magnetization reversal in nanowires. Micromagnetic analysis shows that the domain wall structure is mainly determined by the competition between the demagnetization energy and exchange energy. The wall with vortex magnetization structure in cross-section is energetically more favorable for wires with large diameter. With the reduction of diameter the exchange energy increases. At a critical diameter the vortex structure can not be sustained and the transition from vortex wall to transverse wall occurs. The critical diameters for this transition are about 40 nm for Ni wire and 20 nm for Fe wire, respectively. A series of micromagnetic simulations on the cone-shaped wire confirm the analytical results. The simulations also show that during the reversal process the vortex domain wall moves much faster than the transverse one.

Nucleation in ferromagnetic nanowires—magnetostatics and topology

Magnetization reversal in nanowires can be accomplished locally via thermal nucleation of soliton-antisoliton pairs. It is demonstrated that the total nonlocal magnetostatic energy can be reduced to a local anisotropy if the particle diameter is smaller than the magnetic length scale. Topological restrictions of the curling mode are discussed. Barrier energies for nucleation at sample ends are computed and close agreement with recent experiments on Ni-nanowires is found.