A15 Phase Ta3Sb Thin Films: Direct Synthesis, Charge Transport and Spin-Orbit Torque

TL;DR

This study reports the synthesis, electronic properties, and spin Hall effect measurements of Ta3Sb thin films, revealing a large intrinsic spin Hall conductivity consistent with theoretical predictions, despite some discrepancies due to stoichiometry.

Contribution

First demonstration of direct synthesis of Ta3Sb thin films with A15 structure and measurement of their spin Hall conductivity, bridging experimental results with theoretical predictions.

Findings

Ta3Sb thin films can be synthesized with a large flux ratio window.

The measured spin Hall conductivity ranges from -526 to -1230 (hbar/e) S/cm at 300 K.

Discrepancies with theoretical values are explained by Fermi level shifts due to non-ideal stoichiometry.

Abstract

Ta3Sb is one of the A15 compounds that have been predicted to have giant spin Hall conductivities due to the gapped Dirac-like band crossings in their electronic structures. We use co-sputtering to directly synthesize thin films of Ta3Sb and identify a large window of Ta:Sb flux ratio that permits the formation of single-phase A15 structure. These sputtered films have an actual Ta:Sb atomic ratio of 4:1 as determined from Rutherford backscattering spectrometry. Their high resistivity, at the Mott-Ioffe-Regel limit, suggests that the electron mean free path is comparable to interatomic distances. From harmonic Hall and spin-torque ferromagnetic resonance measurements, the intrinsic spin Hall conductivity of thin film Ta3Sb is estimated to be in the range of -526 to -1230 (hbar/e) S/cm at 300 K, lower in magnitude than the predicted value of -1400 (hbar/e) S/cm. First-principles calculations of the electronic structure show that the discrepancy is consistent with an increase of the Fermi level due to the non-ideal stoichiometry needed to stabilize the A15 structure.