Forming individual magnetic biskyrmions by merging two skyrmions in a centrosymmetric nanodisk

Abstract

When two magnetic skyrmions – whirl-like, topologically protected quasiparticles – form a bound pair, a biskyrmion state with a topological charge of N Sk = ±2 is constituted. Recently, especially the case of two partially overlapping skyrmions has brought about great research interest. Since for its formation the individual skyrmions need to posses opposite in-plane magnetizations, such a biskyrmion cannot be stabilized by the Dzyaloshinskii-Moriya-interaction (DMI), which is the interaction that typically stabilizes skyrmions in non-centrosymmetric materials and at interfaces. Here, we show that these biskyrmions can be stabilized by the dipole-dipole interaction in centrosymmetric materials in which the DMI is forbidden. Analytical considerations indicate that the bound state of a biskyrmion is energetically preferable over two individual skyrmions. As a result, when starting from two skyrmions in a micromagnetic simulation, a biskyrmion is formed upon relaxation. We propose a scheme that allows to control this biskyrmion formation in nanodisks and analyze the individual steps.

Spontaneous skyrmionic lattice from anisotropic symmetric exchange in a Ni-halide monolayer

“…4b. Due to their specific multichiral nature 1,20,53 , no such chiral-degeneracy lifting is observed for the ASk and 2Sk lattices. Our results thus demonstrate that the two-site anisotropy may behave as an emergent chiral interaction for this class of centrosymmetric systems, determining a unique topology and chirality of the spin structure.…”

“…Conversely, 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, in fact, 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 .…”

Biskyrmion lattices in centrosymmetric magnetic films

“…Unlike skyrmions, that have been mostly observed in chiral films, stable biskyrmions lattices have been initially reported down to zero field in two nonchiral films of sufficient thickness: the La 2−2x Sr 1+2x Mn 2 O 7 manganite [24] and the (Mn 1−x Ni x ) 65 Ga 35 half-Heusler alloy [25]. Recent works [26][27][28] provided further experimental and numerical evidence of stable biskyrmions in centrosymmetric magnetic materials.…”

Interplay between Single-Ion and Two-Ion Anisotropies in Frustrated 2D Semiconductors and Tuning of Magnetic Structures Topology

“…The skyrmion formation is primarily driven by competing Heisenberg and Dzyaloshinskii–Moriya (DM) [ 17 ] exchange interactions, the sign of the latter determining the spins rotational direction, in turn dictated by the chiral crystal structure [ 18 , 19 , 20 , 21 ]. Skyrmionic lattices with various—not a priori determined—topologies can instead occur in geometrically frustrated lattices (such as triangular or Kagome), triggered by competing magnetic exchange interactions and assisted by dominant non-chiral interactions, such as easy-axis anisotropy [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], long-range dipole–dipole and/or Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions [ 7 , 30 , 31 , 32 , 33 ], and thermal or quantum fluctuations [ 34 ]. In both cases, the stabilization of skyrmions is often driven by an external magnetic field perpendicular to the magnetic layer (i.e., out-of-plane).…”