Abstract
Magnetic phase transitions are a manifestation of competing interactions whose behavior is critically modified by defects and becomes even more complex when topological constraints are involved. In particular, the investigation of skyrmions and skyrmion lattices offers insight into fundamental processes of topological-charge creation and annihilation upon changing the magnetic state. Nonetheless, the exact physical mechanisms behind these phase transitions remain unresolved. Here, we show numerically that it is possible to collectively reverse the polarity of a skyrmion lattice in a field-induced first-order phase transition via a transient antiskyrmion-lattice state. We thus propose a new type of phase transformation where a skyrmion lattice inverts to another one due to topological constraints. In the presence of even a single defect, the process becomes a second-order phase transition with gradual topological-charge melting. This radical change in the system’s behavior from a first-order to a second-order phase transition demonstrates that defects in real materials could prevent us from observing collective topological phenomena. We have systematically compared ultra-thin films with isotropic and anisotropic Dzyaloshinskii-Moriya interactions (DMIs), and demonstrated a nearly identical behavior for such technologically relevant interfacial systems.
Highlights
The interplay between the symmetric Heisenberg exchange, antisymmetric Dzyaloshinskii-Moriya (DMI)[1] and long-range magnetostatic interactions generates complex spin textures, such as helical, conical, and as shown recently[2,3,4] skyrmionic phases
We start by analyzing the magnetization profile of a Bloch and a Néel skyrmion in zero magnetic field in thin films with Dzyaloshinskii-Moriya interactions (DMIs) and perpendicular magnetic anisotropy (PMA)
Skyrmions are configured in a hexagonal lattice and the global topological charge is equal to the number of skyrmions in the lattice, which in our case is Q = 64
Summary
The interplay between the symmetric Heisenberg exchange, antisymmetric Dzyaloshinskii-Moriya (DMI)[1] and long-range magnetostatic interactions generates complex spin textures, such as helical, conical, and as shown recently[2,3,4] skyrmionic phases. Skyrmions are magnetic solitons that occur on surfaces and interfaces upon rotational-symmetry breaking by either an external magnetic field[5] or perpendicular magnetic anisotropy (PMA)[6]. The sign of topological charge depends on the magnetization polarity of a skyrmion, and on the direction of magnetization winding (vorticity). Multilayers[23,24], skyrmions form even at room temperature and in zero external magnetic field due to strong PMA. It has been shown numerically[25] and experimentally[26] that a new type of magnetic solitons, namely radial vortices, occur in the presence of weak in-plane anisotropy. The exact mechanism of this kind of phase transitions, remains relatively unexplored so far
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
