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Ultrafast switching of antiferromagnetic order by field-derivative torque

Pratyay Mukherjee, Ritwik Mondal

Abstract

Control of magnetic order in antiferromagnets is a central challenge in the development of next-generation spintronic devices. Here, we propose and analyze magnetization switching driven by the field-derivative torque, a torque that originates from the time-derivative of an applied THz pulse acting on the staggered order parameter. Using atomistic spin simulations, we show that the field-derivative torque couples efficiently to the Néel vector, enabling deterministic switching without net spin accumulation. Further, we show that using the circularly polarised THz pulse, the FDT-induced magnetization switching reduces the required THz magnetic field by two-fold. To this end, we compute the switching and non-switching areas as a function of THz pulse width, THz magnetic field, and damping of the antiferromagnetic material. We find that the switching and non-switching areas are completely deterministic in antiferromagnets. Moreover, the switching area increases by about 55% when the FDT is considered.

Ultrafast switching of antiferromagnetic order by field-derivative torque

Abstract

Control of magnetic order in antiferromagnets is a central challenge in the development of next-generation spintronic devices. Here, we propose and analyze magnetization switching driven by the field-derivative torque, a torque that originates from the time-derivative of an applied THz pulse acting on the staggered order parameter. Using atomistic spin simulations, we show that the field-derivative torque couples efficiently to the Néel vector, enabling deterministic switching without net spin accumulation. Further, we show that using the circularly polarised THz pulse, the FDT-induced magnetization switching reduces the required THz magnetic field by two-fold. To this end, we compute the switching and non-switching areas as a function of THz pulse width, THz magnetic field, and damping of the antiferromagnetic material. We find that the switching and non-switching areas are completely deterministic in antiferromagnets. Moreover, the switching area increases by about 55% when the FDT is considered.
Paper Structure (6 sections, 3 equations, 5 figures)

This paper contains 6 sections, 3 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Atomistic Spin Dynamics
  3. Results and Discussions
  4. Conclusions
  5. acknowledgments
  6. DATA AVAILABILITY STATEMENT

Figures (5)

  • Figure 1: Schematic diagram for circularly polarized THz excitation of antiferromagnetic spins in $\rm NiO$. The upward Ni spins are denoted in golden color, while the downward Ni spins are denoted in purple. Red small spheres denote the oxygen atoms.
  • Figure 2: Simulation results of the magnetization dynamics without FDT (Left Panel) and with FDT (Right Panel) for an incident THz pulse having ${\rm B_0}= 8.15$ T, $\sigma = 4$ ps and $\tau = 130$ ps. (a) and (e) show the $y$- and $z$-components of the circularly-polarized THz pulse, (b) and (f) show the $z$-component of the Néel vector, (c) and (g) show the $y$-component of the total magnetization, while (d) and (h) show magnetization dynamics of the individual sublattices.
  • Figure 3: Normalized ${\rm l_z}$ after THz excitation of NiO as a function of THz field amplitude $B_0$ and pulse width $\sigma$. Golden regions (${\rm l_z} = 1$) indicate no reversal, while purple regions (${\rm l_z} = -1$) denote magnetization switching. (a) Without FDT and (b) with FDT.
  • Figure 4: Normalized ${\rm l_z}$ after THz excitation of NiO as a function of THz field amplitude $B_0$ and Gilbert damping $\alpha$ with FDT. Golden regions (${\rm l_z} = 1$) indicate no reversal, while purple regions (${\rm l_z} = -1$) denote switching.
  • Figure 5: The dynamics of total magnetization ${\bf M}$ along the effective torque direction exerted by the THz pulse and the FDT.