Sergey Grytsiuk
Three-dimensional magnetic textures with particle-like properties [1-2] have been recently growing in popularity due to a great potential for innovative spintronic applications [3-5] and brain-inspired computing. However, only little is known about solids where such 3D magnetic solitons may exist and a complete theoretical model for the underlying magnetic interactions is remarkably elusive until now. While, for instance, the basic magnetic properties of the 2D skyrmions are determined by an intricate competition involving the Heisenberg exchange and the chiral relativistic Dzyaloshinskii–Moriya interaction (DMI), such models fail to explain the 3D-magnetic texture of few-nm size observed in MnGe.
Recently, we have discovered a conceptually new class of the magnetic interactions rooted in the so-called topological orbital moment, a Berry-phase effect that results from the orbital motion of the electron in a complex magnetic background [6]. We refer to these interactions as topological–chiral interactions, favouring the emergence of non-coplanar magnetic structures with scalar spin chirality of specific sign even without an external magnetic field. The novel interactions offer fundamentally different opportunities for imprinting chiral magnetism, as they manifest in the scalar chirality of spin arrangements on triangular plaquettes, as opposed to the vector chirality between pairs of spins in the case of DMI. By means of density functional calculations we demonstrate that these interactions are not small but can dominate over the celebrated DMI in selecting the chiral ground state, providing possibly a key for solving the open question of the recently observed complex 3D magnetic structures in B20-type chiral magnet MnGe. In addition, we show that in the continuum limit, the spin-chirality relates to the curvature of the magnetization field and one flavour of the topological–chiral interaction reverts to the Faddeev model [1] with solutions for the 3D magnetic solitons, known as hopfions.
In this talk, I will give brief introduction to the topological–chiral interactions focusing on rigorous derivation based on Multiple scattering theory. Also, I will discuss the role of the novel interactions in stabilising the nontrivial magnetic orders in bulk and thin films of different materials.
[2] N. Manton and P. Sutcliffe, Topological Solitons (Cambridge University Press, Cambridge, England, 2004).
[3] A. M. Kosevich et al., Phys. Rep. 194, 117 (1990).
[4] X. S. Wang et al., PRL 123, 147203 (2019)
[5] Yizhou Liu et al., 124, 127204 (2020)
[6] S. Grytsiuk et al., Nature Comm., 11, 511 (2020)