Antiskyrmions stabilized at interfaces by anisotropic Dzyaloshinskii-Moriya interaction (1702.07573v2)

Abstract: Chiral magnets are an emerging class of topological matter harbouring localized and topologically protected vortex-like magnetic textures called skyrmions, which are currently under intense scrutiny as a new entity for information storage and processing. Here, on the level of micromagnetics we rigorously show that chiral magnets cannot only host skyrmions but also antiskyrmions as least-energy configurations over all non-trivial homotopy classes. We derive practical criteria for their occurrence and coexistence with skyrmions that can be fulfilled by (110)-oriented interfaces in dependence on the electronic structure. Relating the electronic structure to an atomistic spin-lattice model by means of density-functional calculations and minimizing the energy on a mesoscopic scale applying spin-relaxation methods, we propose a double layer of Fe grown on a W(110) substrate as a practical example. We conjecture that ultrathin magnetic films grown on semiconductor or heavy metal substrates with $C_{2v}$ symmetry are prototype classes of materials hosting magnetic antiskyrmions.

• The paper shows that the determinant of the spiralization tensor governs magnetic stability, favoring antiskyrmions over skyrmions when negative.
• Micromagnetic simulations and DFT calculations confirm that anisotropic DMI at C2v symmetry interfaces drives robust antiskyrmion formation.
• The study highlights potential spintronic applications by tuning interface-induced DMI, paving the way for high-density magnetic storage technologies.

Antiskyrmions Stabilized at Interfaces by Anisotropic Dzyaloshinskii-Moriya Interaction

The paper of antiskyrmions and their stabilization in chiral magnetic systems represents a significant advance in the understanding of topological magnetic structures. This paper explores the possibility of stabilizing antiskyrmions at interfaces through anisotropic Dzyaloshinskii-Moriya interaction (DMI). Antiskyrmions are topologically distinct magnetic textures, opposite in charge to the more commonly studied skyrmions. The authors leverage a combination of micromagnetic simulations, density functional theory (DFT), and symmetry analysis to make compelling arguments for the conditions under which antiskyrmions can exist as stable entities.

Theoretical Background

Chiral magnets, such as Fe on a W(110) substrate, can host skyrmions and antiskyrmions, which are stabilized by the DMI that arises due to spin-orbit coupling in systems lacking inversion symmetry. Unlike cubic or bulk DMI, anisotropic DMI at interfaces provides a rich landscape for stabilizing not only skyrmions but also antiskyrmions. The theoretical premise is grounded in variations of the spiralization tensor, which describe the coupling strength of the DMI in different crystallographic directions. The sign and magnitude of the determinant of this tensor critically determine whether skyrmions or antiskyrmions are energetically favorable.

Key Findings

1. Energy Landscape Analysis: The authors rigorously demonstrate that the determinant of the spiralization tensor dictates the stability preference between skyrmions and antiskyrmions. A negative determinant correlates with antiskyrmions becoming the lowest energy configuration over all non-trivial homotopy classes.
2. Symmetry Considerations: Systems with $C_{2v}$ symmetry, such as interfaces between bcc (110) planes, offer an ideal environment for antiskyrmions due to the directional dependence of the DM vectors, which are not purely radial as in the higher symmetry cases. The change in chirality directions supports the formation of antiskyrmions.
3. Micromagnetic and Atomistic Simulations: Spin dynamics simulations confirm that antiskyrmions are stable under zero magnetic field conditions for Fe/W(110), primarily due to the anisotropic contributions to DMI. Intralayer interactions in particular play a dominant role in stabilizing these textures.
4. DFT Calculations: Through DFT analysis, the paper highlights that the anisotropic DMI vectors contribute significantly in the stabilization process and explains the dependence on electronic structure details. For the system studied, the key components of DMI vectors demonstrated compensatory behavior within the interface and the surface layer.

Implications and Future Directions

The ability to stabilize antiskyrmions has several potential applications in spintronics, particularly in the development of high-density information storage systems. With their robust topological nature and exotic dynamics, antiskyrmions provide functionalities not possible with traditional skyrmions. The authors' findings also prompt further theoretical and experimental investigations into materials systems with potential for realizing stable antiskyrmions, especially magnetic films and heterostructures with specific symmetry properties.

The paper advances the understanding of DMI and its role in the stabilization of non-trivial magnetic textures. These insights could pave the way for new paradigms in magnetic device engineering, offering alternative mechanisms for data encoding and retrieval. The exploration and synthesis of materials with controlled DMI properties will be crucial for leveraging antiskyrmion properties in practical applications.

In conclusion, this paper provides a comprehensive framework for understanding the stabilization of antiskyrmions and opens new avenues for future research in the field of chiral magnetism and topologically protected magnetic textures.