We have fabricated and measured single domain wall magnetoresistance devices with sub-20 nm gap widths using a novel combination of electron beam lithography and helium ion beam milling. The measurement wires and external profile of the spin valve are fabricated by electron beam lithography and lift-off. The critical bridge structure is created using helium ion beam milling, enabling the formation of a thinner gap (and so a narrower domain wall) than that which is possible with electron beam techniques alone. Four-point probe resistance measurements and scanning electron microscopy are used to characterize the milled structures and optimize the He ion dose. Successful operation of the device as a spin valve is demonstrated, with a 0.2% resistance change as the external magnetic field is cycled.
The critical dimensions used in CMOS technology and RAM memory are conventionnaly defined by photo-lithography and hence limited in size by the wavelength of the light. Methods to create smaller dimensions, such as electron beam writing, exist, but are prohibitively expensive for production purposes. Self-assembly of nanostructures is a fundamental from-bottom-to-top technique in which solid structures of nanometer dimensions are synthesized by self-organized processes from constituents like atoms, molecular beams, or macro-molecules. In the current project, magnetic nanostructures are defined by electrodeposition on Si through a mask of a self assembled template from poly(styrene) latex. The samples will be characterized by magnetic and magneto-resistance measurements and will provide unique information on giant and domain-wall magnetoresistance. Application as MRAM is envisioned.