We report an initial experimental survey of spin-Hall torques generated by the rare-earth metals Gd, Dy, Ho, and Lu, along with comparisons to first-principles calculations of their spin Hall conductivities. Using spin torque ferromagnetic resonance (ST-FMR) measurements and DC-biased ST-FMR, we estimate lower bounds for the spin-Hall torque ratio, ξSH, of ≈ 0.04 for Gd, ≈ 0.05 for Dy, ≈ 0.14 for Ho, and ≈ 0.014 for Lu. The variations among these elements are qualitatively consistent with results from first principles (density functional theory, DFT, in the local density approximation with a Hubbard-U correction). The DFT calculations indicate that the spin Hall conductivity is enhanced by the presence of the partially-filled f orbitals in Dy and Ho, which suggests a strategy to further strengthen the contribution of the f orbitals to the spin Hall effect by shifting the electron chemical potential.
@article{arxiv.1612.01927,
title = {Spin-Hall Torques Generated by Rare-Earth (Lanthanide) Thin Films},
author = {Neal Reynolds and Priyamvada Jadaun and John T. Heron and Colin L. Jermain and Jonathan Gibbons and Robyn Collette and R. A. Buhrman and D. G. Schlom and D. C. Ralph},
journal= {arXiv preprint arXiv:1612.01927},
year = {2017}
}