Magnetoresistance in constrained domain walls

In magnetic materials, domains of magnetic orientation in opposite direction are often alternated. The transition in orientation between these domains, the domain wall, is not abrupt but spatially extended. When a current is passed through the magnetic material, the resistance of the material is dependent on whether such domain wall exists, which in its turn depends on the external magnetic field. This magneto-resistance is larger for smaller domain walls. Although the domain wall width is in principle a materials parameter, by patterning the magnetic sample into certain nanostructures, it is possible to constrain the domain wall such that its width is smaller than its natural unconstrained width.We have measured domain wall magnetoresistance in a single lithographically constrained domain wall. An H-shaped Ni nanobridge was fabricated by either e-beam lithography or a combination of e-beam lithography and helium ion milling. The two sides of the device are both single magnetic domains showing independent magnetic switching. The connection between the sides constrains the domain wall when the sides line up antiparallel. The magnetoresistance curve clearly identifies the magnetic configurations that are expected from a spin-valve like structure.The room temperature domain wall measurements give a magneto-resistance ratio of 0.1 % for the 94 nm and 0.2 % for the 32 nm constriction. Although these values are in itself small, they are the first results on lithographically prepared single domain spin valves. The single-layered device might allow for easier fabrication and space savings for high dense storage applications as compared to giant magneto-resistance and tunneling magneto-resistance. Also, the research of spin-based logic devices will benefit from the physical understanding that follows from measurements of magneto-resistance devices without material interface