  Spin Hall effect (SHE) induced reversal of perpendicular magnetization has
attracted significant interest, due to its potential to lead to low power
memory and logic devices. However, the switching requires an assisted in-plane
magnetic field, which hampers its practical applications. Here, we introduce a
novel approach for external-field-free spin Hall switching of a perpendicular
nanomagnet by utilizing a local dipolar field arising from an adjacent in-plane
magnetic layer. Robust switching of perpendicular CoFeB nanopillars in a
dipole-coupled composite stack is experimentally demonstrated in the absence of
any external magnetic field, in consistent with the results of micromagnetic
simulation. Large in-plane compensation field of about 135 Oe and out-of-plane
loop shift of about 45 Oe / 10 7 A cm-2 are obtained in the nanopillar devices
with composite structure. By performing micromagnetic simulations, we confirm
the composite external-field-free switching strategy can also work for a 10 x
10 nm2 circular pillar. Compared with other proposed methods for
external-field-free spin Hall switching of perpendicular magnetization, the
dipole-coupled composite structure is compatible with a wide range of spin Hall
systems and perpendicular magnetic tunnel junctions, paving the way towards
practical SHE-based MRAM and logic applications.
