  Strain-clocked dipole-coupled nanomagnetic logic is an energy-efficient
Boolean logic paradigm whose progress has been stymied by its propensity for
high error rates. In an effort to mitigate this problem, we have studied the
effect of nanomagnet geometry on error rates, focusing on elliptical and
cylindrical geometries. We had previously reported that the out-of-plane
excursion of the magnetization vector during switching creates a precessional
torque that is responsible for high switching error probability in elliptical
nanomagnet geometries. The absence of this torque in cylindrical magnets
portends lower error rates, but our simulations show that the error rate
actually does not improve significantly compared to elliptical magnets while
the switching becomes unacceptably slow. Here, we show that dipole coupled
nanomagnetic logic can offer relatively high reliability (switching error
probability < 10^-8), moderate clock speed (~ 100 MHz) and 2-3 orders of
magnitude energy saving compared to CMOS devices, provided the shape anisotropy
energy barrier of the magnet is increased to at least ~5.5 eV to allow
engineering a stronger dipole coupling between neighboring nanomagnets.
