Enhanced interfacial Dzyaloshinskii-Moriya interaction and isolated skyrmions in the inversion-symmetry-broken Ru/Co/W/Ru films

Abstract

An enhancement of the spin-orbit effects arising on an interface between a ferromagnet (FM) and a heavy metal (HM) is possible through the strong breaking of the structural inversion symmetry in the layered films. Here, we show that an introduction of an ultrathin W interlayer between Co and Ru in Ru/Co/Ru films enables to preserve perpendicular magnetic anisotropy (PMA) and simultaneously induce a large interfacial Dzyaloshinskii-Moriya interaction (iDMI). The study of the spin-wave propagation in the Damon-Eshbach geometry by Brillouin light scattering spectroscopy reveals the drastic increase in the iDMI value with the increase in W thickness (tW). The maximum iDMI of −3.1 erg/cm2 is observed for tW = 0.24 nm, which is 10 times larger than for the quasi-symmetrical Ru/Co/Ru films. We demonstrate the evidence of the spontaneous field-driven nucleation of isolated skyrmions supported by micromagnetic simulations. Magnetic force microscopy measurements reveal the existence of sub-100-nm skyrmions in the zero magnetic field. The ability to simultaneously control the strength of PMA and iDMI in quasi-symmetrical HM/FM/HM trilayer systems through the interface engineered inversion asymmetry at the nanoscale excites new fundamental and practical interest in ultrathin ferromagnets, which are a potential host for stable magnetic skyrmions.

Enhancement of perpendicular magnetic anisotropy and Dzyaloshinskii–Moriya interaction in thin ferromagnetic films by atomic-scale modulation of interfaces

“…All these asdeposited films had in-plane anisotropy only and minimal surface roughness. Recently, it has been shown that Pt, Ta, and Ru have a negative IDMI at the bottom interface, leading to partial cancellation of the effective IDMI (D eff ) if a ferromagnet layer is sandwiched between them 46,47 . We defined by BLS that these three reference samples have negative effective values of the IDMI: D eff = −0.83, −0.48, and −0.34 erg/cm 2 , respectively.…”

Readable High-Speed Racetrack Memory Based on an Antiferromagnetically Coupled Soft/Hard Magnetic Bilayer

“…For example, the uniaxial-anisotropy constant can be too small to maintain the PMA or be as large as 10 6 J/m 3 . The DMI constant can be between 0 and 3 mJ/m 2 [25], depending on the composition and thickness of the HM or FM layers and the annealing treatment. All the parameters used in our simulation are in an experimentally achievable range.…”

“…Therefore, it is enough that one HM layer has spin Hall effect [18]. Some compositions of HM/FM satisfy the above requirement, such as Pt/Co and Co/Ir/Pt [26], and W/Co and Co/Ru/W [25].…”

Микромагнитные И Магнитооптические Свойства Пленочных Структур Вида Ферромагнетик/Тяжелый Металл

“…Зачастую в качестве тяжелого металла используют благородные металлы, такие как Pt, Pd, Ru и др., в этом случае пленки обладают повышенной коррозионной стойкостью. Помимо этого, благодаря наличию межфазного обменного взаимодействия Дзялошинского−Мория [3] между атомами металлов, в таких пленках возможно существование стабильных при комнатной температуре наноразмерных магнитных структур -скирмионов [4]. Применение пленок ферромагнетик/тяжелый металл в ряде приборов спинтроники, например, слоев CoPt в конструкции спинового светоизлучающего диода [5], позволяет существенно снизить диапазон рабочих магнитных полей вплоть до возможности функционирования прибора без приложения внешнего магнитного поля за счет использования остаточной намагниченности материала.…”