  Recently there is considerable interest to realize efficient and low-cost
true random number generators (RNGs) for practical applications. One important
way is through the use of bistable magnetic tunnel junctions (MTJs). Here we
study the magnetization dynamics of an MTJ, with a focus to realize efficient
random bit generation under the assumption that the orientation dependence of
the energy of the nanomagnet is described by two perpendicular in-plane
anisotropies. We find that a high rate of random bit generation is achievable
away from the pure easy-axis situation by tuning a single parameter $H_z$ so
that it is either (a) toward a barrierless-like single easy plane situation
when $H_z$ reduces to zero, or (b) toward a stronger easy plane situation when
$H_z$ becomes increasingly negative where transitions between low energy states
are confined in the stronger easy plane that contains the saddle points. We
find that the MTJs maintain their fast magnetization dynamical characteristics
even in the presence of a magnetic field. Our findings provide a valuable guide
to achieving efficient generation of probabilistic bits for applications in
probabilistic computing.
