Abstract
Magnetic topological defects can store and carry information. Replacement of extended defects, such as domain walls and Skyrmion tubes, by compact magnetic particles that can propagate in all three spatial directions may open an extra dimension in the design of magnetic memory and data processing devices. We show that such objects can be found in iron langasite, which exhibits a hierarchy of non-collinear antiferromagnetic spin structures at very different length scales. We derive an effective model describing long-distance magnetic modulations in this chiral magnet and find unusual two- and three-dimensional topological defects. The order parameter space of our model is similar to that of superfluid 3He-A, and the particle-like magnetic defect is closely related to the Shankar monopole and hedgehog soliton in the Skyrme model of baryons. Mobile magnetic particles stabilized in non-collinear antiferromagnets can play an important role in antiferromagnetic spintronics.
Highlights
The topology of defects in ordered states of matter is governed by the order parameter describing spontaneous symmetry breaking at a phase transition[1]
The importance of a larger order parameter space in triangular magnets with the 120° ordering for critical phenomena and topological defects was noted already some time ago[25]
An additional ingredient discussed in this paper is the lack of inversion symmetry in the crystal lattice, which gives rise to DM interactions resulting in additional long-period modulations of the 120° spin structure
Summary
The topology of defects in ordered states of matter is governed by the order parameter describing spontaneous symmetry breaking at a phase transition[1]. We discuss a realistic material that can host threedimensional (3D) magnetic Skyrmions—non-singular defects which, unlike the Skyrmion tubes, have a finite size in all three spatial directions These magnetic particles can transfer information in all directions, stimulating the design of three-dimensional spintronic devices. Shankar monopole has been recently realized in the Bose–Einstein condensate of trapped spin-1 particles by application of time-dependent and spatially inhomogeneous magnetic fields[24]. This defect is, unstable and has a short lifetime. Higher-dimensional order parameter spaces can be realized in magnetic materials, in particular, antiferromagnets with triangle-based spin lattices showing a non-collinear 120° ordering of spins in the triangles described by an SO(3) matrix[25,26]. We show that the same DM interactions can stabilize more complex modulated states as well as unusual topological magnetic defects, in particular, the magnetic particles carrying 3D Skyrmion topological charge and an associated Hopf number
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