Abstract
Topological spin structures, such as magnetic skyrmions, hold great promises for data storage applications, thanks to their inherent stability. In most cases, skyrmions are stabilized by magnetic fields in non-centrosymmetric systems displaying the chiral Dzyaloshinskii-Moriya exchange interaction, while spontaneous skyrmion lattices have been reported in centrosymmetric itinerant magnets with long-range interactions. Here, a spontaneous anti-biskyrmion lattice with unique topology and chirality is predicted in the monolayer of a semiconducting and centrosymmetric metal halide, NiI2. Our first-principles and Monte Carlo simulations reveal that the anisotropies of the short-range symmetric exchange, when combined with magnetic frustration, can lead to an emergent chiral interaction that is responsible for the predicted topological spin structures. The proposed mechanism finds a prototypical manifestation in two-dimensional magnets, thus broadening the class of materials that can host spontaneous skyrmionic states.
Highlights
Topological spin structures, such as magnetic skyrmions, hold great promises for data storage applications, thanks to their inherent stability
This state consists in a triangular lattice of antibiskyrmions (A2Sk) characterized by a topological charge ∣Q∣ = 2 with associated vorticity m = − 2, as shown in Fig. 1; see refs. 18,40,41 for further insights about skyrmionic spin structures
We found that metastable multi-q skyrmionic states, that may occur in frustrated magnets, can stabilize as ground-state with well-defined topology and chirality in the presence of competing two-site anisotropies characterized by noncoplanar principal axes
Summary
Topological spin structures, such as magnetic skyrmions, hold great promises for data storage applications, thanks to their inherent stability. In geometrically frustrated centrosymmetric lattices (such as triangular or Kagome), possible skyrmion-lattice states triggered by competing exchange interaction manifest with various topologies[11,12,13,14,15], as there is no mechanism determining a priori their topology and chirality[16,17,18,19,20] These states, generally arise from nonchiral interactions, such as easy-axis magnetic anisotropy, long-range dipole–dipole and/or Ruderman– Kittel–Kasuya–Yosida (RKKY) interactions, and thermal or quantum fluctuations[11,12,13,14,15,21]. A spontaneous skyrmion-lattice state has been proposed so far only in itinerant magnets displaying amplitude variations of the magnetization[4], where its microscopic origin was attributed to long-range effective four-spin and higher-spin interactions that arise from conduction electrons[6,22,23,24,25]
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