Helium ion beam milling to create a nano-structured domain wall magnetoresistance spin valve

• Published in: Nanotechnology 2012-10, Vol.23 (39), p.395302-395302
• Main Authors: Wang, Yudong, Boden, S A, Bagnall, D M, Rutt, H N, de Groot, C H
• Format: Article
• Language: English
• Subjects: Devices; Domain walls; Electron beam lithography; Helium; Ion beams; Magnetoresistance; Nanostructure; Spin valves
• ISSN: 0957-4484; 1361-6528
• DOI: 10.1088/0957-4484/23/39/395302

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 helium ion beam milling efficiency as extracted from electrical resistance measurements is 0.044 atoms ion, about half the theoretical value. The gap in the device is limited to a maximum of 20 nm with this technique due to sub-surface swelling caused by injected ions which can induce catastrophic failure in the device. The fine patterning capabilities of the helium ion microscope milling technique indicate that sub-5 nm constriction widths could be possible.