Orthorhombic distortion and rectangular skyrmion crystal in a centrosymmetric tetragonal host

Abstract

We theoretically investigate the stability of a rectangular skyrmion crystal without fourfold rotational symmetry under an orthorhombic distortion in centrosymmetric tetragonal magnets. The results are obtained by numerically simulated annealing for an effective spin model with competing interactions in momentum space and magnetic anisotropy. By constructing the low-temperature phase diagram while changing the interaction ratio arising from the orthorhombic distortion, we find that the rectangular skyrmion crystal remains stable in an external magnetic field against distortion. We show that the degree of fourfold rotational symmetry tends to recover when the magnetic field is increased. The relevance to the skyrmion-hosting material EuAl4 is also discussed.

Uniaxial Distortion Effect on Magnetic Skyrmion Crystals in a Frustrated Triangular-Lattice System

“…3(c). A similar phase sequence has also been found in the centrosymmetric tetragonal compound EuAl 4 , where the importance of the competing interactions in momentum space was pointed out [30,32]. The present result indicates that the momentum-resolved DM interaction also becomes a source of inducing multiple SkX phases in noncentrosymmetric magnets.…”

“…As a result, we find that the competing interactions in momentum space give rise to phase transitions among the different types of SkX phases. We show that the structural transition from the distorted triangular SkX (DT-SkX) to the S-SkX occurs as found in EuNiGe 3 [39], and that from the distorted S-SkX (DS-SkX) to the S-SkX occurs as found in EuAl 4 [30,32] depending on the degree of frustration in momentum space. Our results provide an important essence to induce multiple SkX phases, which will be useful for further exploration of topological spin textures in noncentrosymmetric magnets.…”

“…Another example is a centrosymmetric tetragonal magnet EuAl 4 . In contrast to MnSi and Co 8 Zn 8 Mn 4 , two types of SkXs, which were identified as the S-SkX and a rhombic SkX, have been observed as thermodynamics phases by changing the magnetic field [30][31][32][33]. In this compound, the model calculations have shown that the competition of the interactions in momentum space that arise from the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mediated by itinerant electrons [34][35][36] or frustrated exchange interactions plays an important role [30,32,33].…”

“…In contrast to MnSi and Co 8 Zn 8 Mn 4 , two types of SkXs, which were identified as the S-SkX and a rhombic SkX, have been observed as thermodynamics phases by changing the magnetic field [30][31][32][33]. In this compound, the model calculations have shown that the competition of the interactions in momentum space that arise from the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mediated by itinerant electrons [34][35][36] or frustrated exchange interactions plays an important role [30,32,33]. More recently, such structural transition of the equilibrium SkX phases has also been observed in a polar magnet EuNiGe 3 , where the long-range Dzyaloshinskii-Moriya (DM) interaction [37,38], as well as the RKKY interaction, contributes to the emergence of the multiple SkXs [39].…”

Zero-Field Skyrmion, Meron, and Vortex Crystals in Centrosymmetric Hexagonal Magnets

“…A magnetic skyrmion crystal (SkX) with nontrivial topological properties has been extensively studied since its direct experimental observation in 2009 [1,2]. Although it was originally discovered in noncentrosymmetric magnets [1][2][3][4], where the competition between the ferromagnetic exchange interaction and the Dzyaloshinskii-Moriya (DM) interaction [5,6] plays an important role [7][8][9][10], its appearance in centrosymmetric magnets has been clarified through the observations for various bulk materials, such as Gd 2 PdSi 3 [11][12][13][14], Gd 3 Ru 4 Al 12 [15,16], GdRu 2 Si 2 [17][18][19][20][21][22] and EuAl 4 [23][24][25][26]. Simultaneously, a variety of SkXs without relying on the DM interaction have been theoretically studied for various lattice structures [27], such as square [28][29][30][31], triangular [32][33][34][35][36][37], and cubic lattices [38].…”