AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Thursday Sessions
       Session MI+NS-ThM

Invited Paper MI+NS-ThM5
Magnetic Quantum Cellular Automata

Thursday, October 28, 1999, 9:40 am, Room 618/619

Session: Patterned or Self-Assembled Magnetic Nanostructures
Presenter: R.P. Cowburn, University of Cambridge, UK
Authors: R.P. Cowburn, University of Cambridge, UK
D.K. Koltsov, University of Cambridge, UK
A.O. Adeyeye, University of Cambridge, UK
M.E. Welland, University of Cambridge, UK
Correspondent: Click to Email
Nanometre scale magnetic particles (nanomagnets) are promising candidates for implementing Magnetic Quantum Cellular Automata (MQCA) architectures. In order to use nanomagnets in this way their magnetic properties must be fully understood. In particular, the conditions required to obtain a single domain state (and hence the ability to signal a 1 or a 0) must be established. Furthermore, in order to achieve room temperature operation of MQCA, magnetostatic coupling between nanomagnets must be understood and controlled. We have performed a detailed experimental and theoretical investigation into these aspects of nanomagnetism. We have used high resolution electron beam lithography to fabricate nanomagnets in the size range 40-500nm with elliptical or circular geometries. We find that the shape anisotropy introduced by the elliptical form greatly stabilises the single domain state; in the absence of any ellipticity, all of the nanomagnets greater than approximately 100nm in diameter collapse into a flux closing vortex state. We have then fabricated chains of sub-100nm nanomagnets with gaps as small as 15nm between neighbouring edges. We find experimental evidence for strong magnetostatic coupling. We have thus achieved the conditions necessary for a MQCA implementation, i.e. a well defined digital state even at room temperature which can be switched by interactions from neighbouring cells. We have used the finding described above to make a working room temperature MQCA gate. CMOS electronic signals are interfaced directly to the magnetic system by passing a small current through a gold track underneath part of the gate; outputs are currently read by focusing a laser beam onto a magnetic test point and using the magneto-optic Kerr effect to monitor its magnetic state. The gate achieves an overall power gain (and hence the ability to work at room temperature and to fan out) by an applied oscillating magnetic field.