Electrical currents flowing in ferromagnetic materials are spin-polarised as a result of the spin-dependent band structure. When the spatial direction of the polarisation changes, in a domain structure, the electrons must somehow accommodate the necessary change in direction of their spin angular momentum as they pass through the wall. Reflection, scattering, or a transfer of angular momentum onto the lattice are all possible outcomes, depending on the circumstances. This gives rise to a variety of different physical effects, most importantly a contribution to the electrical resistance caused by the wall, and a motion of the wall driven by the spin-polarised current. Historical and recent research on these topics is reviewed. Contents PAGE 1. Introduction5862. Spin-polarised current587 2.1. Tunnelling current spin polarisation589 2.2. Ballistic current spin polarisation592 2.3. Diffusive current spin polarisation5933. Magnetic Domain Walls598 3.1. Basics of domain walls598 3.1.1. Domain wall thickness and...

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Spin-polarised currents and magnetic domain walls

High-resolution magnetic patterning of a thin CoFe layer has been performed by irradiation using a focused-ion-beam system. Features <50nm wide were formed reproducibly. The irradiated pattern comprised sets of alternating 3.0- and 1.0-μm-long magnetic wires, 100 nm wide. During magnetization reversal, the longer wires reversed at a lower field resulting in the formation of an ordered array of domains with density 10μm−1 supporting antiparallel magnetization. The ability to create domains at predefined locations is important both for fundamental studies and technological applications.

Nanopatterning of a thin ferromagnetic CoFe film by focused-ion-beam irradiation

We have investigated the evolution of magnetic spin states and in-plane magnetic anisotropy in arrays of elongated Ni80Fe20 rings. Large area (4×4mm2) elongated Ni80Fe20 nanorings of thickness in the range from 5to60nm were fabricated using deep ultraviolet lithography at 248nm exposing wavelength. The magnetic spin states and the magnetization reversal processes are strongly dependent on the ring thickness and in-plane magnetic anisotropy due to the elongation of the rings. Our experimental results are in a very good agreement with micromagnetic simulations.

Spin state evolution and magnetic anisotropy of elongated Ni80Fe20 nanorings

We report on the control of magnetization reversal in exchange-biased Co/CoO nanorings resulting from the competition between field-cooling-induced unidirectional anisotropy at the Co/CoO interface and shape anisotropy of the elongated Co nanorings. We observed that the magnetization reversal mechanisms and magnitudes of exchange bias fields are strongly dependent on the strength and orientation of the cooling field relative to the major axis of the nanorings. Our results demonstrate a convenient technique to control the magnetization reversal modes in ferromagnetic nanorings.

Controlling the magnetization reversal in exchange-biased Co/CoO elongated nanorings

α-Fe 2 O 3 nanostructured ring arrays with different ring sizes were fabricated by solution-dipping on a colloidal monolayer template. The magnetic properties of the arrays are investigated. An abnormal magnetic step region was observed in the hysteresis loop at room temperature, showing existence of a steady “Vortex” state in α-Fe 2 O 3 ring arrays at room temperature. However, at a low temperature (50 K), the step region disappeared. Also, no step region is found from Fe ring array with the similar morphology to that of α-Fe 2 O 3 . This is attributed to the weak dependence of hysteresis loop on size and morphology of the single ring for α-Fe 2 O 3 at room temperature.

Magnetic step regions in α-Fe2O3 nanostructured ring arrays

Patterned Permalloy submicron-size structures have been fabricated by e-beam lithography in the shape of a ring with a tip. A tip was intentionally added into the ring as a geometrical defect to interrupt the continuity of the magnetization, which aligns along the ring, in order to pin the domain wall. Magnetic switching and reversal process have been measured by the magnetoresistance measurement. The switching field about 260 Oe was obtained. At the remanent state, there was a 0.21% difference in the magnetoresistance between the angles of 90° and 0° that was equivalent to the domain wall magnetoresistance. By applying an external field, the domain wall moved along the ring under a lower field (100 Oe), which is smaller than the switching field. A drop (0.24%) in the resistance between the angle of 70°–120° has been observed that means the domain wall was moving into the voltage measuring region during the rotation.

https://ir.nctu.edu.tw:443/bitstream/11536/26738/1/000221657900070.pdf

J. S. Chen

Papers

Magnetic switching and reversal process in a tip ring structure