Effects of Anisotropic Strain on Spin–Orbit Torque Produced by the Dirac Nodal Line Semimetal IrO₂

Abstract

We report spin-torque ferromagnetic resonance studies of the efficiency of the damping-like (ξ DL ) spin−orbit torque exerted on an adjacent ferromagnet film by current flowing in epitaxial ( 001) and ( 110) IrO 2 thin films. IrO 2 possesses Dirac nodal lines (DNLs) in the band structure that are gapped by spin− orbit coupling, which could enable a very high spin Hall conductivity, σ SH . We find that the (001) films do exhibit exceptionally high ξ DL ranging from 0.45 at 293 K to 0.65 at 30 K, which sets the lower bounds of σ SH to be 1.9 × 10 5 and 3.75 × 10 5 Ω −1 m −1 , respectively, 10 times higher and of opposite sign than the theoretical prediction. Furthermore, ξ DL and σ SH are substantially reduced in anisotropically strained (110) films. We suggest that this high sensitivity to anisotropic strain is because of changes in contributions to σ SH near the DNLs.

Spin Pumping and Inverse Spin Hall Effect in Iridium Oxide

“…The obtained values are comparable to the value reported for epitaxially grown crystalline (001) IrO 2 films (1.9 at 300 K [ 33 ] ). The value obtained for IrO 2 is higher in comparison to many other high SOC materials like Pt, W, Ta, Bi 2 Se 3 , etc.…”

Modulation of Spin–Orbit Torque from SrRuO3 by Epitaxial‐Strain‐Induced Octahedral Rotation

“…[45,47] The possible contributing factors are discussed in Note S7 of the Supporting Information. In Note S8 of the Supporting Information, we also evaluate that the observed differences in ξ DL,HHV and ξ FMR across substrates are less likely to arise from the interface of SrRuO 3 /Py, though oxidation of Py [48] might influence the interfacial transparency [36,49] of SrRuO 3 /Py. In order to interpret the origin of SOT generated by SrRuO 3 , we examine the temperature (T) dependence of ξ DL,HHV .…”

Dimensionality-driven metal–insulator transition in spin–orbit-coupled IrO2

“…These values are in good agreement with other previously reported for epitaxial films. 29,30,31 The low temperaturedependent contribution ρ(T) fits well to a T 2 -dependence indicating that the electron-electron scattering dominates the temperature dependent part of the electrical resistivity, i.e., a typical Fermi liquid behavior.…”