Correlation between the spin Hall angle and the structural phases of early 5d transition metals

TL;DR

This study investigates how the structural phases of early 5d transition metals influence their spin Hall angles, revealing that amorphous-like phases yield larger spin Hall effects due to higher resistivity and conductivity.

Contribution

It demonstrates the correlation between amorphous-like structures and enhanced spin Hall angles in early 5d transition metals, highlighting the importance of phase control.

Findings

Largest spin Hall angles occur in amorphous-like phases.

Crystalline phases show reduced spin Hall angles.

Amorphous-like phases have higher resistivity and spin Hall conductivity.

Abstract

We have studied the relationship between the structure and the spin Hall angle of the early 5d transition metals in X/CoFeB/MgO (X=Hf, Ta, W, Re) heterostructures. Spin Hall magnetoresistance (SMR) is used to characterize the spin Hall angle of the heavy metals. Transmission electron microscopy images show that all underlayers are amorphous-like when their thicknesses are small, however, crystalline phases emerge as the thickness is increased for certain elements. We find that the heavy metal layer thickness dependence of the SMR reflects these changes in structure. The spin Hall angle largest |\theta$_{SH}$| of Hf, Ta, W and Re (~0.11, 0.10, 0.23 and 0.07, respectively) is found when the dominant phase is amorphous-like. We find that the amorphous-like phase not only possesses large resistivity but also exhibits sizeable spin Hall conductivity, which both contribute to the emergence of the large spin Hall angle.