Abstract
The effects of competing magnetic interactions in stabilizing different spin configurations are drawing renewed attention in order to unveil emerging topological spin textures and to highlight microscopic mechanisms leading to their stabilization. The possible key role of the two-site exchange anisotropy in selecting specific helicity and vorticity of skyrmionic lattices has only recently been proposed. In this work, we explore the phase diagram of a frustrated localized magnet characterized by a two-dimensional centrosymmetric triangular lattice, focusing on the interplay between the two-ion anisotropy and the single-ion anisotropy. The effects of an external magnetic field applied perpendicularly to the magnetic layer, are also investigated. By means of Monte Carlo simulations, we find an abundance of different spin configurations, going from trivial to high-order Q skyrmionic and meronic lattices. In closer detail, we find that a dominant role is played by the two-ion over the single-ion anisotropy in determining the planar spin texture; the strength and the sign of single ion anisotropy, together with the magnitude of the magnetic field, tune the perpendicular spin components, mostly affecting the polarity (and, in turn, the topology) of the spin texture. Our analysis confirms the crucial role of the anisotropic symmetric exchange in systems with dominant short-range interactions; at the same time, we predict a rich variety of complex magnetic textures, which may arise from a fine tuning of competing anisotropic mechanisms.
Highlights
The competition between different magnetic interactions, leading to the so-called frustration, is a key ingredient for the stabilization of noncollinear and noncoplanar magnetic configurations
Our previous firstprinciples based investigation [40] on NiI2 monolayer revealed that its magnetic properties are ruled by: (i) strong magnetic frustration arising from competing nearest-neighbor (J 1iso ) ferromagnetic (FM) and third-nearest neighbor (J 3iso ) anti-ferromagnetic (AFM) exchange interactions; very weak easy-plane single-ion anisotropy against highly anisotropic symmetric exchange, both driven by spin-orbit coupling (SOC)
We have theoretically investigated the effects of competing single-ion and two-ion anisotropies in a triangular lattice with strong magnetic frustration, as occurring in monolayers of van der Waals nickel dihalides
Summary
The competition between different magnetic interactions, leading to the so-called frustration, is a key ingredient for the stabilization of noncollinear and noncoplanar magnetic configurations. Anisotropic interactions play a crucial role in the formation of exotic and topological spin textures, such as Bloch or Neél type skyrmions and anti-skyrmions, most commonly having a topological charge | Q| equal to one [1,2,3]. The different types of isolated two-dimensional (2D) topological spin textures are primarily characterized by the polarity p and vorticity m, whose product, Q = m · p, defines their topology. The polarity is associated with the out-of-plane magnetization profile, when moving from the core of the topological object to its edge (to infinity in a continuous description of isolated object); the vorticity is determined by the in-plane magnetization rotation and it is referred to as the winding number, allowing only for integer values [8,14]. (anti)skyrmions, which are characterized by reversed magnetization directions when comparing the core with its edge, corresponding to a spin configuration
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