  Low barrier nanomagnets have attracted a lot of research interest for their
use as sources of high quality true random number generation. More recently,
low barrier nanomagnets with tunable output have been shown to be a natural
hardware platform for unconventional computing paradigms such as probabilistic
spin logic. Efficient generation and tunability of high quality random bits is
critical for these novel applications. However, current spintronic random
number generators are based on superparamagnetic tunnel junctions (SMTJs) with
tunability obtained through spin transfer torque (STT), which unavoidably leads
to challenges in designing concatenated networks using these two terminal
devices. The more recent development of utilizing spin orbit torque (SOT)
allows for a three terminal device design, but can only tune in-plane
magnetization freely, which is not very energy efficient due to the needs of
overcoming a large demagnetization field. In this work, we experimentally
demonstrate for the first time, a stochastic device with perpendicular magnetic
anisotropy (PMA) that is completely tunable by SOT without the aid of any
external magnetic field. Our measurements lead us to hypothesize that a tilted
anisotropy might be responsible for the observed tunability. We carry out
stochastic Landau-Lifshitz-Gilbert (sLLG) simulations to confirm our
experimental observation. Finally, we build an electrically coupled network of
two such stochastic nanomagnet based devices and demonstrate that finite
correlation or anti-correlation can be established between their output
fluctuations by a weak interconnection, despite having a large difference in
their natural fluctuation time scale. Simulations based on a newly developed
dynamical model for autonomous circuits composed of low barrier nanomagnets
show close agreement with the experimental results.
