  Probabilistic (p-) bits implemented with low energy barrier nanomagnets
(LBMs) have recently gained attention because they can be leveraged to perform
some computational tasks very efficiently. Although more error-resilient than
Boolean computing, p-bit based computing employing LBMs is, however, not
completely immune to defects and device-to-device variations. In some tasks
(e.g. binary stochastic neurons for machine learning and p-bits for population
coding), extended defects, such as variation of the LBM thickness over a
significant fraction of the surface, can impair functionality. In this paper,
we have examined if unavoidable geometric device-to-device variations can have
a significant effect on one of the most critical requirements for probabilistic
computing, namely the ability to "program" probability with an external agent,
such as a spin-polarized current injected into the LBM. We found that the
programming ability is fortunately not lost due to reasonable device-to-device
variations. The little variation in the probability versus current
characteristic that reasonable device variability causes can be suppressed
further by increasing the spin polarization of the current. This shows that
probabilistic computing with LBMs is robust against small geometric variations,
and hence will be "scalable" to a large number of p-bits.
