  Magnetization reversal of a perpendicular ferromagnetic free layer by
spin-orbit torque (SOT) is an attractive alternative to spin-transfer torque
(STT) switching in magnetic random-access memory (MRAM) where the write process
involves passing a high current across an ultrathin tunnel barrier. A small
symmetry-breaking bias field is usually needed for deterministic SOT switching
but it is impractical to generate the field externally for spintronic
applications. Here, we demonstrate robust zero-field SOT switching of a
perpendicular Co90Fe10 (CoFe) free layer where the symmetry is broken by
magnetic coupling to a second in-plane exchange-biased CoFe layer via a
nonmagnetic Ru spacer. The preferred magnetic state of the free layer is
determined by the current polarity and the nature of the interlayer exchange
coupling (IEC). Our strategy offers a scalable solution to realize
bias-field-free SOT switching that can lead to a generation of SOT-based
devices, that combine high storage density and endurance with potentially low
power consumption.
