Realization of Ground-State Artificial Skyrmion Lattices at Room Temperature

Abstract

The topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. Here, we demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from the dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. The imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.

Giant Dzyaloshinskii-Moriya interaction in Rashba superlattices

“…Generally, in order to stabilize skyrmions at room temperature, multilayer structures with repetitive stacking of FM/HM bilayer are utilized because multistacking of the bilayer unit easily provide the PMA and the sizable DMI at the same time, both of them arising from the same physical origin, i.e., interfacial SOC [9,10]. In this respect, Co/Pd and Co/Pt interfaces are one of the well-known material combinations providing both the PMA and the DMI originating from interfaces, resulting in stable magnetic skyrmions in [Co/Pd] superlattices [11,12]. With the same manner of such a AB-type multi-stacking structure composed of several nanometer-thick layers as illustrated in Fig.…”

Elucidating proximity magnetism through polarized neutron reflectometry and machine learning

“…Neutron reflectometry facilitates structural characterization of multilayered materials by probing their nuclear and magnetic depth profiles at device-relevant spatial scales, enabling the study of hidden interfaces in a broad range of nanostructured and thin film systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Leveraging the interaction of spin-polarized neutrons with magnetic moments, polarized neutron reflectometry (PNR) is particularly well-suited to detecting magnetic interfacial phenomena [17][18][19][20][21][22][23][24] such as the magnetic proximity effect.…”

Magnetotransport studies of heterostructures based on transition metals and their oxides

“…A recent trend in the skyrmion-based study is incorporating skyrmion into advanced artificial structures for both fundamental studies and spintronic devices, such as racetrack memory [132][133][134], logic devices [135,136], and skyrmion magnonic crystals [137,138]. Since these skyrmions could be stabilized by interfacial interaction without DMI, these skyrmions are often referred to as artificial skyrmions [139][140][141][142][143][144][145]. Moreover, when skyrmions have an extended center region where all the spins are aligned (Figure 3.1e).…”

“…These skyrmions are sometimes named skyrmion bubbles [124,146,147]. One of the most widely used artificial structures is the nano-patterned heterostructure [139][140][141][142]148,149]. These nanostructures contain nanodisks with artificial sizes, thicknesses, and shapes.…”

“…Skyrmion bubbles, nucleating right under these nanodisks, obtain additional tunability from the varied structure. Moreover, skyrmion bubbles in the nanostructure could interplay with each other and form a crystal-like group, referred to as artificial skyrmion lattice [139,141] or skyrmion crystal [142,144,148]. The idea of integrating artificial crystal order into skyrmions expands the spintronic research frontier [137,138].…”