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Register a new userHelical and skyrmion lattice phases in three-dimensional chiral magnets: Effect of anisotropic interactions
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In this work, we study the magnetic orders of the classical spin model with the anisotropic exchange and Dzyaloshinskii-Moriya interactions in order to understand the uniaxial stress effect in chiral magnets such as MnSi. Variational zero temperature (T) calculated results demonstrate that various helical orders can be developed depending on the magnitude of the interaction anisotropy, consistent with the experimental observations at low T. Furthermore, the creation and annihilation of the skyrmions by the uniaxial pressure can be also qualitatively reproduced in our Monte Carlo simulations. Thus, our work suggests that the interaction anisotropy tuned by applied uniaxial stress may play an essential role in modulating the magnetic orders in strained chiral magnets.
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We study two-body interactions of magnetic skyrmions on the plane and apply them to a (mostly) analytic description of a skyrmion lattice. This is done in the context of the solvable line, a particular choice of a potential for magnetic anisotropy and Zeeman terms, where analytic expressions for skyrmions are available. The energy of these analytic single skyrmion solutions is found to become negative below a critical point, where the ferromagnetic state is no longer the lowest energy state. This critical value is determined exactly without the ambiguities of numerical simulations. Along the solvable line the interaction energy for a pair of skyrmions is repulsive with power law fall off in contrast to the exponential decay of a purely Zeeman potential term. Using the interaction energy expressions we construct an inhomogeneous skyrmion lattice state, which is a candidate ground states for the model in particular parameter regions. Finally we estimate the transition between the skyrmion lattice and an inhomogeneous spiral state.
We develop a theory of the magnetic field-induced formation of Skyrmion crystal state in chiral magnets in two spatial dimensions, motivated by the recent discovery of the Skyrmionic phase of magnetization in thin film of Fe$_{0.5}$Co$_{0.5}$Si and in the A-phase of MnSi. Ginzburg-Landau functional of the chiral magnet re-written in the CP$^1$ representation is shown to be a convenient framework for the analysis of the Skyrmion states. Phase diagram of the model at zero temperature gives a sequence of ground states, helical spin $rightarrow$ Skyrme crystal $rightarrow$ ferromagnet, as the external field $B$ increases, in good accord with the thin-film experiment. In close analogy with Abrikosovs derivation of the vortex lattice solution in type-II superconductor, the CP$^1$ mean-field equation is solved and shown to reproduce the Skyrmion crystal state.
Topologically protected swirl of the magnetic texture known as the Skyrmion has become ubiqui- tous in both metallic and insulating chiral magnets. Meanwhile the existence of its three-dimensional analogue, known as the magnetic monopole, has been suggested by various indirect experimental sig- natures in MnGe compound. Theoretically, Ginzburg-Landau arguments in favor of the formation of a three-dimensional crystal of monopoles and anti-monopoles have been put forward, however no microscopic model Hamiltonian was shown to support such a phase. Here we present strong numerical evidence from Monte Carlo simulations for the formation of a rock-salt crystal structure of monopoles and anti-monopoles in short-period chiral magnets. Real-time simulation of the spin dynamics suggests there is only one collective mode in the monopole crystal state in the frequency range of several GHz for the material parameters of MnGe.
The phase diagrams of the frustrated classical spin model with Dzyaloshinskii-Moriya (DM) interaction on the Shastry-Sutherland (S-S) lattice are studied by means of Monte Carlo simulation. For ferromagnetic next-nearest-neighboring (J2) interactions, the introduced exchange frustration enhances the effect of the DM interaction, which enlarges the magnetic field-range with the skyrmion lattice phase and increases the skyrmion density. For antiferromagnetic J2 interactions, the so-called 2q phase (two-sublattice skyrmion crystal) and the spin-flop phase are observed in the simulated phase diagram, and their stabilizations are closely dependent on the DM interaction and J2 interaction, respectively. The simulated results are qualitatively explained from the energy landscape, which provides useful information for understanding the intriguing phases in S-S magnets.
Magnetic skyrmions are stable topological spin textures with significant potential for spintronics applications. Merons, as half-skyrmions, have been discovered by recent observations, which have also raised the upsurge of research. The main purpose of this work is to study further the lattice forms of merons and skyrmions. We study a classical spin model with Dzyaloshinskii-Moriya interaction, easy-axis, and in-plane magnetic anisotropies on the honeycomb lattice via Monte Carlo simulations. This model could also describe the low-energy behaviors of a two-component bosonic model with a synthetic spin-orbit coupling in the deep Mott insulating region or two-dimensional materials with strong spin-orbit coupling. The results demonstrate the emergence of different sizes of spiral phases, skyrmion and vortex superlattice in absence of magnetic field, furthered the emergence of field-induced meron and skyrmion superlattice. In particular, we give the simulated evolution of the spin textures driven by the magnetic field, which could further reveal the effect of the magnetic field for inducing meron and skyrmion superlattice.
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