Optically induced spin-dependent diffusive transport in the presence of spin-orbit interaction for all-optical magnetization reversal

Mehrdad Elyasi and Hyunsoo Yang

Phys. Rev. B 94, 024417 – Published 14 July 2016

Abstract

We have considered the effect of different spin-orbit interaction mechanisms on the process of demagnetization under the influence of short-pulse lasers. All-optical magnetization reversal of perpendicularly magnetized thin films can occur if there are sufficient strong spin-Hall, skew scattering, and Rashba interactions. In the presence of spin-orbit interactions, the transient charge currents provide the generation of transverse-spin currents and accumulations, which eventually exert spin-transfer torque on the magnetization. By combining the optically excited spin-dependent diffusive transport with the spin and charge currents due to skew scattering, spin-Hall, inverse spin-Hall, and Rashba interactions into a numerical model, we demonstrate a possibility of ultrafast all-optical magnetization reversal. This understanding provokes intriguing, more in-depth experimental studies on the role of spin-orbit interaction mechanisms in optimizing structures for all-optical magnetization reversal.

Received 23 March 2016
Revised 27 June 2016

DOI:https://doi.org/10.1103/PhysRevB.94.024417

Physics Subject Headings (PhySH)

Magnetization switching Spin-orbit coupling Ultrafast phenomena

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Mehrdad Elyasi and Hyunsoo Yang^*

Department of Electrical and Computer Engineering, National University of Singapore, 117576 Singapore

^*eleyang@nus.edu.sg

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 94, Iss. 2 — 1 July 2016

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) The schematic of a FM/ NM bilayer and the laser spatial absorption pattern. The points in the FM are the impurities. (b) Top and side view of the in-plane spin current (in the radial direction) with spin polarization along $\hat{φ}$ , induced due to SHE in NM from $J_{c, z} \hat{z}$ with spin polarization of $S_{z} \hat{z}$ . (c) Spin currents due to skew scattering of $J_{c, r} \hat{r}$ with spin polarization of $S_{z} \hat{z}$ . Panels marked by numbers 1 and 2 refer to the two possible spin currents. The rightmost panel shows the side view of the spin current shown in panel 2. (d) ISHE-induced charge currents due to $J_{c, z}$ with transverse-spin polarizations of $S_{r}$ or $S_{φ}$ . (e) Spin current parallel to $\hat{φ}$ induced by $J_{c, r}$ due to the Rashba interaction at the FM/NM interface. The green (dashed black) arrows indicate direct (inverse) scattering. Black, red, blue, and pink arrows indicate charge current, spin polarization before scattering, spin current, and spin polarization after scattering, respectively. Dark blue (dark green) balls are nonscattered (scattered) electrons.
Reuse & Permissions
Figure 2
(a) Spatial average (average over $0 < r < R_{las}$ and $t_{N M} \leq z < d_{tot})$ of the temporal evolution of ${\vec{S}}_{neq}$ and the change in $m_{s}$ in the FM layer $({\vec{S}}_{a v g}$ and $Δ m_{z}$ , respectively) up to 160 fs. (b–d) The radial average (average over $0 < r < R_{las})$ of the spatiotemporal distribution of ${\vec{S}}_{neq}$ in the $\hat{r}, \hat{φ}$ , and $\hat{z}$ directions, respectively. (e) The radial average of the spatiotemporal distribution of the change in $m_{s}, Δ m_{z}$ .
Reuse & Permissions
Figure 3
(a) $S_{φ}, S_{z}$ , and $Δ m_{z}$ for $t_{N M} = 2.5 nm$ (continuous line, case 1), 2 nm (dashed line, case 2), and 3 nm (dotted line, case 3). (b) $S_{φ}, S_{z}$ , and $Δ m_{z}$ for $Δ_{s d}$ $(Δ_{s s}) = 1 fs$ (continuous line), 2 fs (dashed line), and 5 fs (dotted line). (c) $S_{φ}, S_{z}$ , and $Δ m_{z}$ for $Γ_{s k} = - 0.3$ (dashed line, case 4), $Γ_{s k} = - 0.1$ (continuous line), $Γ_{s k} = 0$ (dash-dotted line, case 5), and $Γ_{s k} = 0.3$ (dotted line, case 6). (d) $S_{φ}, S_{z}$ , and $Δ m_{z}$ for $a = 1$ (dashed line, case 7), $a = 2$ (continuous line), and $a = 4$ (dotted line, case 8). (e) $S_{φ}, S_{z}$ , and $Δ m_{z}$ for $λ = 5$ nm (dashed line, case 9), $λ = 15 nm$ (continuous line), and $λ = 25 nm$ (dotted line, case 10). For (a–e), $t_{F M} = 1 nm, N_{r} = 5$ , and the continuous line represents a similar case $[t_{N M} = 2.5 nm, Δ_{s d}$ $(Δ_{s s}) = 1 fs, Γ_{s k} = - 0.1, a = 2$ , and $λ = 15 nm]$ . (f) The value of $Δ_{s d}$ that the magnetization reversal becomes possible while we keep $M_{s} + min (Δ m_{z}) = 0.1 μ_{B} / atom$ for cases 1–10. (The error bar for $Δ_{s d}$ is $\pm 0.01 fs$ and dot sizes reflect this error bar.)
Reuse & Permissions
Figure 4
(a) $S_{φ}$ and $S_{z}$ for $a = 1$ , 1.2, 1.5, and 2. (b) The value of $Δ_{s d}$ that the magnetization reversal becomes possible while we keep $M_{s} + min (Δ m_{z}) = 0.1 μ_{B} / atom$ for the cases in (a) (the error bar for $Δ_{s d}$ is $\pm 0.01 fs$ and dot sizes reflect the error bar). (c–d) The spatiotemporal distribution of ${\vec{S}}_{neq}$ in the $\hat{φ}$ direction in the NM (averaged over $0 < z \leq d_{N M})$ for $a = 1$ and $a = 2$ , respectively. (e–f) The spatiotemporal distribution of ${\vec{S}}_{neq}$ in the $\hat{φ}$ direction in the FM (average over $d_{N M} < z < d_{tot})$ for $a = 1$ and $a = 2$ , respectively.
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics