Field-free spin-orbit torque switching of Cr-induced perpendicular magnetization

Current-induced spin-orbit torque (SOT) switching in a heterostructure with perpendicular magnetic anisotropy (PMA) has attracted great attention, as a new writing method for spintronic devices. However, this highly attractive switching scheme is often accompanied by an unfavorable external magnetic field. In this work, we show that the 3d Cr, without any heavy metals and the MgO layer, can induce strong interfacial PMA and deliver deterministic SOT switching. Most importantly, we demonstrate field-free SOT switching in 3d Cr without any complex schemes, including asymmetrical layers, pattern structure, and additional ferromagnetic or antiferromagnetic layers. We show that the underlying cause for the deterministic field-free switching lies in the slanted columnar microstructure for the otherwise uniform thin films. The direction of oblique columnar structure dictates the up and down orientations of the PMA layer, resulting in polarity-controlled field-free SOT switching [1]. Our results uncover the significant role of 3d materials and shed light on field-free SOT magnetization switching.