Ferrimagnetic Skyrmions in Topological Insulator/Ferrimagnet Heterostructures

Abstract

Magnetic skyrmions are topologically nontrivial chiral spin textures that have potential applications in next‐generation energy‐efficient and high‐density spintronic devices. In general, the chiral spins of skyrmions are stabilized by the noncollinear Dzyaloshinskii–Moriya interaction (DMI), originating from the inversion symmetry breaking combined with the strong spin–orbit coupling (SOC). Here, the strong SOC from topological insulators (TIs) is utilized to provide a large interfacial DMI in TI/ferrimagnet heterostructures at room temperature, resulting in small‐size (radius ≈ 100 nm) skyrmions in the adjacent ferrimagnet. Antiferromagnetically coupled skyrmion sublattices are observed in the ferrimagnet by element‐resolved scanning transmission X‐ray microscopy, showing the potential of a vanishing skyrmion Hall effect and ultrafast skyrmion dynamics. The line‐scan spin profile of the single skyrmion shows a Néel‐type domain wall structure and a 120 nm size of the 180° domain wall. This work demonstrates the sizable DMI and small skyrmions in TI‐based heterostructures with great promise for low‐energy spintronic devices.

Recent Progress in Proximity Coupling of Magnetism to Topological Insulators

“…Apart from QAHI and axion insulators, ferromagnetic insulator–topological insulator–ferromagnetic insulator (FMI–TI–FMI) have also proven to be the playground of other exotic new phases such as topological Hall effect (THE), which is also known as geometric Hall effect (GHE); [ 197,207,208 ] planar Hall effect (PHE); [ 159 ] and skyrmions. [ 209,210 ] These topics are also discussed below. The versatility of these heterostructures, also often makes it possible to achieve more than one type of such quantum phases in the same device.…”

“…Adapted by permission. [ 210 ] Copyright 2020, The Authors. Published by Wiley‐VCH Verlag GmbH & Co. KGaA.…”

“…directly imaged skyrmions for the first time in a ferrimagnet‐TI heterostructure of GdFeCo–(Bi,Sb) 2 Te 3 at room temperature. [ 210 ] The strong interfacial DMI, resulting from spin–orbit coupling (SOC) of TI and breaking of inversion‐symmetry at the interface, facilitates superexchange interaction between the magnetic moments of GdFeCo, stabilizing magnetic skyrmions (as shown in Figure 10a). Figure 10b–e shows a color scale plot of the magnetization of the same structure, obtained through scanning transmission X‐ray microscopy (STXM).…”

Imaging the spin chirality of ferrimagnetic Néel skyrmions stabilized on topological antiferromagnetic Mn3Sn

“…For potential spintronic applications, interfacially asymmetric multilayers of stacking order heavy metal 1 /ultrathin ferromagnet/heavy metal 2 (HM 1 /FM/HM 2 ), where HM 2 can be either a different material or implying a different interface characteristic due to growth, are particularly promising for hosting roomtemperature Néel skyrmions [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In these multilayers, standard HM layers (such as Pt, Ta, W, Ir, and Pd) or topological insulators (TIs) with strong spin-orbit couplings (SOCs) are generally required for mediating the interfacial Dzyaloshinskii-Moriya interaction (iDMI) that subsequently determines the spin chirality of Néel-type spin textures [20][21][22][23][24][25][26][27][28]. In this regard, it is important to explore alternative Néel-skyrmion-hosting multilayers without directly involving the standard HM layers.…”

Topological insulators-based magnetic heterostructures

“…Equivalently, the strong SOC combined with inversion symmetry breaking in TI-based magnetic heterostructures can also provide the noncollinear Dzyaloshinskii-Moriya interaction (DMI) at the interface, hence facilitating the formation of non-trivial topological spin textures (e.g., magnetic skyrmions) and exotic topological/geometric Hall effects [98,99]. Experimentally, the trace of magnetic skyrmions can be found among modulation-doped MTI, MTI/FM and MTI/AFM heterostructures [100--102], and their unique properties has been characterized by magnetotransport, X-ray photoemission electron microscopy (XPEEM) and Scanning Transmission X-ray microscopy (STXM), as summarized in Figure 11.…”