  In this article we analyze by modeling two possible mechanisms for
magnetization switching using spin orbit torques, which have been reported to
cause field-free deterministic switching in experiments. Here we compare the
field-free magnetization switching due to a tilt of the anisotropy direction
against the use of an antiferromagnetic bias field. Simple results obtained
analytically show that a bias field not only causes the magnetization reversal
but also reduces the corresponding energy barrier. The critical current
required for magnetization switching is analyzed on the basis of a macrospin
model. It is shown that although the field-free deterministic switching caused
by a tilt of the anisotropy is more robust than the bias field in the
development of memory elements, a compromise between requirements has to be
adopted when selecting the parameters for specific applications.
