Effect of crystallinity on spin-orbit torque in 5$\textit{d}$ iridium oxide IrO$_{2}$

TL;DR

This study investigates how the crystallinity of IrO₂ thin films influences spin-orbit torque efficiency, revealing that higher crystallinity enhances electrical resistivity and dampinglike SOT, with nearly constant spin Hall conductivity across different structures.

Contribution

It demonstrates the impact of crystallinity on spin-current generation in IrO₂, highlighting the intrinsic nature of the spin Hall effect in different structural states.

Findings

Dampinglike SOT exceeds fieldlike SOT in all samples.

Electrical resistivity and DL SOT efficiency increase with crystallinity.

Spin Hall conductivity remains nearly constant across different crystallinity states.

Abstract

The 5$\textit{d}$ transition-metal oxides provide an intriguing platform for generating an efficient spin current due to a unique electronic structure dominated by 5d electrons with strong spin-orbit coupling. Here, we report on the effect of crystallinity on current-driven spin-orbit torque (SOT) in binary 5$\textit{d}$ iridium oxide IrO$_{2}$ thin films by controlling amorphous, polycrystalline, and epitaxial states. By conducting harmonic Hall measurement in bilayers composed of ferromagnetic Co$_{20}$Fe$_{60}$B$_{20}$ and IrO$_{2}$, we find that dampinglike (DL) SOT is larger than fieldlike SOT for all the samples. We also demonstrate that both electrical resistivity and the DL SOT efficiency increase in order of epitaxial, polycrystalline, and amorphous IrO$_{2}$. Despite their different electrical conductivities, spin Hall conductivities of the three states of the IrO$_{2}$ layer are found to be nearly constant, which is consistent with the intrinsic regime of the spin Hall effect scaling relation. Our results highlight the important role that crystallinity plays in the spin-current generation, leading to the potential technological development of spintronic devices based on the 5$\textit{d}$ transition-metal oxides.