Estudo da dinâmica da parede de domínio transversal em nanofios magnéticos

Abstract

The understanding of the processes involving the magnetization of ferromagnets becomes increasingly necessary in the face of recent technological applications in magnetic media, reading and writing heads and MRAMs. The study of magnetic nanowires reveals the presence of vortex domain walls or transverse domain walls that can be transported to different regions without deformation, generating a great potential for technological application. The domain wall manipulation in the nanowire is made by applying a magnetic field or spin-polarized current. Controlling the movement of domain walls in magnetic nanowires is fundamental to its applicability in memory technologies and logic devices. In this work, using numerical simulations, we present a study of the dynamics of the “head-to-head” transverse domain wall in magnetic nanowires made of Permalloy-79. In the simulations the nanowires are modeled by a Hamiltonian that takes into account the exchange interaction and dipolar interaction and the dynamics of the system is governed by Landau-Lifshitz-Gilbert equations. The domain wall moves under the influence of pulses of magnetic field. Thus, we analyzed the influence of the thickness and width of the nanowire and the amplitude of the magnetic field in the domain wall velocity. We propose the inclusion of a magnetic impurity by changing the exchange constant J to J0 between a site with impurity and its neighbors. The magnetic impurity can behave like a pinning or scattering site to the domain wall depending on the variation of the exchange constant J0 in relation to the value of reference J. This behavior can be of great interest to control the position of the domain wall. We studied the behavior of the interaction potential between impurity and domain wall. Varying the position of the impurity we observed that the interaction energy increases when it is near to the south pole of the domain wall favoring the pinning or scattering of the wall. We observed that the magnetic impurity affects the domain wall velocity. We performed a study of the magnetic field required for depinning the domain wall which is pinned to a magnetic impurity. We established a relation between the depinning magnetic field and the width of the nanowire. We also observed that under the influence of a pulse of magnetic field above the Walker field the domain wall can reverse its polarity when achieving attractive impurity and reverse the direction of propagation. We believe that a potential technological application in memory devices can be the use of magnetic impurities lithographically inserted in magnetic nanowires to control the positions of the domain walls.