Large enhancement of spin-orbit torques in Pd/CoFeB: The role of boron

Abstract

The conversion of charge current into pure spin current based on the spin Hall effect provides a new way of spin injection and manipulation in novel spintronic architectures. The realization of a large conversion efficiency between the charge and spin currents is a crucial issue for its applications. Here we report a giant enhancement of spin Hall angle (SHA) in palladium through boron engineering. We measure a large SHA of 0.16 in palladium, with perpendicular magnetic anisotropy in the Pd/CoFeB-based structure compared to the Pd/CoFe-based structure ($\mathrm{SHA}=0.02$). Combined with theoretical calculations, it is found that both intrinsic and extrinsic spin Hall effects have been significantly enhanced through the introduction of boron. Taking into account the incorporation of boron in the thin films, the enhanced SHA is attributed to significant microscopic and electronic changes in the Pd host metal. This finding illustrates a crucial role of boron in manipulating spin-orbit torques. Together with high conductivity and long spin diffusion length, this work makes Pd a promising candidate for spintronic devices with magnetization switching by current pulse injection.