Shape engineering of dipole-coupled nanomagnets for magnetic logic devices

Magnetic logic devices are, in principle, capable of transmitting and processing binary information in an entirely magnetic way. Magnetic quantum-dot cellular automata (MQCA) (R.P. Cowburn and M.E. Welland, Science vol. 287, p. 1466, 2000; G. Csaba et al., IEEE Trans on Nanotechnology vol. 1, p. 209, 2002) realize logic functionality based on arrays of dipole-coupled nanomagnets. Recent experimental studies investigated the correlation length of antiferromagnetic ordering on chains of coupled single-domain ferromagnets (R.P. Cowburn, Phys. Rev. B vol. 65, p. 092409, 2002; A. Imre et al., Proc. IEEE-NANO 2003). Switching-field variations of the nanomagnets was identified as a critical issue during the ordering process. We present a combined experimental and theoretical study on arrays of closely-spaced magnetic dots with varying shapes in the size of 70-300 nm. The goal of our study is to identify those shapes which yield the longest correlation lengths for MQCA applications.