Chirality Switching in Ferromagnetic Nanostructures Via Nanosecond Electric Pulses

Abstract

The stability of magnetism in reduced dimensions has become a major scientific agenda in the pursuit of implementing magnetic nanostructures as functional components in spintronic devices. Methods to probe and control magnetization states of such structures in a deterministic manner include use of spin polarized currents, photon absorption, and relatively recently, electric fields that tailor magnetoelectric coupling in multiferroic based structures. In theory, a short electric pulse is able to generate localized magnetic fields that can couple to the local magnetic dipoles electrodynamically. Here, using the Landau–Lifshitz–Gilbert formalism of magnetism dynamics combined with continuum Maxwell relations, the response of a ferromagnetic permalloy nanodisc to nanosecond electric field pulses is studied. The dynamics of the magnetic order of the nanodiscs during this process are examined and discussed. Ferromagnet nanodiscs, when below a critical size and in the absence of any external field, relax to a vortex phase as the ground state due to the demagnetizing field. Simulations demonstrate that the planar chirality of such a ferromagnet nanodisc can be switched via a time‐wise asymmetric electric field pulse on the order of a few ns duration that generates radially varying tangential magnetic fields. These fields couple to the vortex state of the nanodisc ferromagnet electrodynamically, revealing an effective and robust method to control chirality.

Size driven barrier to chirality reversal in electric control of magnetic vortices in ferromagnetic nanodiscs

“…For both the conductor and insulator limit considered, a half cycle, time dependent electrical pulse signal, E ( t ) of the form given in eqn (6) is applied along the normal of the discs to induce chirality reversal 20,46 given as: E ( t ) = E 0 sin 2 (π t / τ d ) k̂ where E 0 is the amplitude of the pulse and τ d is the pulse width ( τ d = 1 ns were chosen in all simulations). We designed two sets of pulses with two different amplitudes E 0 1 ≈ 2 V nm −1 and E 0 2 ≈ 3 V nm −1 given in Fig.…”

“…For both the conductor and insulator limit considered, a half cycle, time dependent electrical pulse signal, E(t ) of the form given in eqn ( 6) is applied along the normal of the discs to induce chirality reversal 20,46 given as:…”

“…28 We have recently shown via micromagnetic simulations that it could be possible to use ns duration electric pulses to control chirality in ferromagnetic nanodiscs. 20…”

“…5 Detection of the vortex order in ferro- magnetic structures via state-of-the-art techniques has led to an ever-increasing insight into the conditions under which they stabilize. The inference from these efforts aided in proposing ways to manipulate the vortex states such as applying magnetic fields and pulses, 3,[13][14][15][16] spin polarized currents, 10,17,18 electric field pulses, 19,20 and use of optical signals 21 and, lately, as chiral magnet-superconductor hybrids to open up new possibilities for their adaptation for use as information storage media and topological quantum devices. 22 Asymmetry in lateral dimensions could aid in the effective switching of chirality of ferromagnets where specific sites act as nucleation centers, which has been pursued in thin films 8,[23][24][25][26][27] however, these methods require additional processes at reduced dimensions.…”

“…28 We have recently shown via micromagnetic simulations that it could be possible to use ns duration electric pulses to control chirality in ferromagnetic nanodiscs. 20 A number of other methods pertaining to electric control of ferromagnetism in reduced dimensions tailoring the magnetoelectric coupling have also proven useful, 29,30 for new device proposals along with works reporting electric control of skyrmions and spin dynamics at domain walls. [31][32][33] In this paper, we study the reversal of the chirality of vortex states in ferromagnetic nanodiscs under an electric pulse using the permalloy Ni 50 Fe 50 as an exemplary case.…”