Evidence for Dyakonov-Perel-like Spin Relaxation in Pt

Ryan Freeman, Andrei Zholud, Zhiling Dun, Haidong Zhou, and Sergei Urazhdin

Phys. Rev. Lett. 120, 067204 – Published 9 February 2018

Abstract

We utilize nanoscale spin valves with Pt spacer layers to characterize spin relaxation in Pt. Analysis of the spin lifetime indicates that Elliott-Yafet spin scattering is dominant at room temperature, but an unexpected intrinsic Dyakonov-Perel-like spin relaxation becomes dominant at cryogenic temperatures. We also observe suppression of spin relaxation in a Pt layer interfaced with a ferromagnet, likely caused by the competition between the effective exchange and spin-orbit fields.

Received 17 July 2017
Revised 30 October 2017

DOI:https://doi.org/10.1103/PhysRevLett.120.067204

Physics Subject Headings (PhySH)

Exchange interaction Ferromagnetism Giant magnetoresistance Spin diffusion Spintronics

Spin valves

Resistivity measurements

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Ryan Freeman¹, Andrei Zholud¹, Zhiling Dun², Haidong Zhou², and Sergei Urazhdin¹

¹Department of Physics, Emory University, Atlanta, Georgia 30322, USA
²Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA

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Issue

Vol. 120, Iss. 6 — 9 February 2018

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Images

Figure 1
(a) Resistance vs applied field for a sample without Pt spacer, at room temperature (RT), $T = 295 K$ . Inset: schematic of the studied nanopillars, with Py layers shown in black, Cu in orange, and Pt in white. (b) Symbols: $Δ R$ , scaled by the MR of the reference sample without Pt spacer, vs Pt thickness $d$ , at RT. Dashed curve: exponential fit to the data. Dotted curve: calculation based on the Valet-Fert theory. (c) Spin diffusion length vs temperature, determined by fitting $Δ R (d)$ with Eq. (1). (d) Interfacial spin-loss factor vs temperature, obtained by fitting $Δ R (d)$ with Eq. (1) (symbols), and by minimizing the difference between the MR data and the Valet-Fert calculations (curve).
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Figure 2
(a) Bulk resistivity (right scale) and the momentum relaxation time (left scale) vs temperature for the studied Pt films. (b) Spin relaxation time vs temperature determined from the data of Fig. 1. (c) Spin relaxation time vs momentum relaxation time. Symbols: data, curve: fitting with a superposition of EY and DP-like contributions, as described in the text. (d) Temperature dependence of the contributions to spin relaxation from DP-like and EY mechanisms, as labeled, determined from the fitting in panel (c).
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Figure 3
(a) Measured (symbols) and calculated (curves) MR vs temperature for the standard spin valve nanopillar with $d = 1 nm$ (circles and solid curve), and for the nanopillar with the structure Py(10)Pt(1)Cu(4)Py(5) (triangles and dotted curve). For the latter, the calculation includes only the EY contribution to spin relaxation. The MR is normalized by its value at RT. (b) Symbols: magnetic correlation length in Pt vs temperature, from Ref. [32]. Curve: dependence expected based on the Curie-Weiss law.
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Figure 4
Interplay between magnetism and intrinsic spin-orbit interaction. The spin of electron in Pt precesses around the effective field ${\vec{H}}_{eff} = {\vec{H}}_{SO} + {\vec{H}}_{ex}$ , where ${\vec{H}}_{SO}$ is the effective spin-orbit field determined by the electron’s momentum $\vec{k}$ , and ${\vec{H}}_{ex}$ is the effective exchange field due to either proximity-induced magnetism or magnetic fluctuation in Pt. The electron’s spin is shown by a bold circled arrow. (a) If $H_{SO}$ dominates, precessional dephasing suppresses the spin polarization and/or magnetization fluctuation. (b) If $H_{ex}$ dominates, the precession angle for electron spins aligned with ${\vec{H}}_{ex}$ is small, suppressing the DP-like spin relaxation.
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