Magnetic octupole p-bits in chiral antiferromagnets: Towards robust and ultra-fast probabilistic computing

The emerging field of antiferromagnetic spintronics promises next generation information processing devices with ultrafast speeds and ultralow energy requirements. But technological adaptation of antiferromagnetic (AFM) devices over ferromagnetic (FM) devices has remained limited due to a key advantage of ferromagnets: the ability to electrically readout the state of a FM through tunnel magneto resistance (TMR). However, with the recent theoretical prediction and experimental observervation of signatures of TMR in non-collinear chiral AFMs with D0₁₉ crystal symmetry (Mn₃X family), chiral AFMs have emerged as a particularly promising material for AFM spintronics. Here we propose to use nanodots of non-collinear chiral AFM as building blocks of a probabilistic computer, the p-bits. In chiral AFM, the order parameter characterizing the state of the magnet and its TMR is given by the octupole moment. Through stochastic LLG equation simulations, we show that strong exchange fields in chiral AFMs lead to ultrafast picosecond fluctuations of octupole moment in the nanodots. We derive analytical expressions for thermal fluctuation speeds in both low and high barrier regimes for the nanodots and show that the chiral AFM nanodots fluctuate an order of magnitude faster than easy plane FM nanodots in both regimes. We further show that the ultrafast fluctuation speeds of chiral AFM nanodots can be translated into robustness of p-circuits against manufacturing and temperature variations in individual p-bits.