Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf broken vertical bar CoFeB broken vertical bar MgO structures

WOS: 000381155200037We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf broken vertical bar CoFeB broken vertical bar MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above similar to 7 nm. Although there might be a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure. Published by AIP Publishing.NSF Nanosystems Engineering Research Center for Translational Applications of Nanoscale Multiferroic Systems (TANMS); FAME Center, one of six centers of STARnet, a Semiconductor Research Corporation (SRC) program - MARCO; DARPAUnited States Department of DefenseDefense Advanced Research Projects Agency (DARPA); TUBITAK "The Scientific and Technological Research Council of Turkey"Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); Cukurova University (Adana/Turkey)Cukurova University [FEF2013D31]This work was partially supported by the NSF Nanosystems Engineering Research Center for Translational Applications of Nanoscale Multiferroic Systems (TANMS). This work was also supported in part by the FAME Center, one of six centers of STARnet, a Semiconductor Research Corporation (SRC) program sponsored by MARCO and DARPA. We would further like to acknowledge the collaboration of this research with the King Abdul-Aziz City for Science and Technology (KACST) via The Center of Excellence for Green Nanotechnologies (CEGN). M.A. would like to acknowledge TUBITAK "The Scientific and Technological Research Council of Turkey" for his financial support during this work. This work was also partially supported by Cukurova University (Adana/Turkey) under the Project No. of 2013, FEF2013D31