  Recent work [1,2] suggests that ferromagnetic reversal with spin transfer
torque (STT) requires more current in a system in the presence of DMI than
switching a typical ferromagnet of the same dimensions and perpendicular
magnetic anisotropy (PMA). However, DMI promotes stabilization of skyrmions and
we report that when the perpendicular anisotropy is modulated (reduced) for
both the skyrmion and ferromagnet, it takes much smaller current to reverse the
fixed skyrmion than to reverse the ferromagnet in the same time, or the
skyrmion reverses much faster than the ferromagnet at similar levels of
current. We show with rigorous micromagnetic simulations and energy portraits
that the skyrmion switching proceeds along a different path at very low PMA
which results in a significant reduction in the spin current required or time
required for reversal. This can have potential for memory application where a
relatively simple modification of the standard STT-RAM to include a heavy metal
adjacent to the soft magnetic layer and with appropriate design of the tunnel
barrier can lead to energy efficient and fast magnetic memory device based on
the reversal of fixed skyrmions.
