Boundary twists, instabilities, and creation of skyrmions and antiskyrmions

Abstract

We formulate and study the general boundary conditions dictating the magnetization profile in the vicinity of an interface between magnets with dissimilar properties. Boundary twists in the vicinity of an edge due to Dzyaloshinskii-Moriya interactions have been first discussed in [Wilson et al., Phys. Rev. B 88, 214420 (2013)] and in [Rohart and Thiaville, Phys. Rev. B 88, 184422 (2013)]. We show that in general case the boundary conditions lead to the magnetization profile corresponding to the Néel, Bloch, or intermediate twist. We explore how such twists can be utilized for creation of skyrmions and antiskyrmions, e.g., in a view of magnetic memory applications. To this end, we study various scenarios how skyrmions and antiskyrmions can be created from interface magnetization twists due to local instabilities. We also show that a judicious choice of Dzyaloshinskii-Moriya tensor (hence a carefully designed material) can lead to local instabilities generating certain types of skyrmions or antiskyrmions. The local instabilities are shown to appear in solutions of the Bogoliubov-de-Gennes equations describing ellipticity of magnon modes bound to interfaces. In one considered scenario, a skyrmion-antiskyrmion pair can be created due to instabilities at an interface between materials with properly engineered Dzyaloshinskii-Moriya interactions. We use micromagnetics simulations to confirm our analytical predictions.

Controlled Creation of Quantum Skyrmions

“…Skyrmion lattices have been experimentally realized in bulk magnetic systems such as MnSi [7], Fe 0.5 Co 0.5 Si [8] and FeGe [9] and at interfaces of, e.g., Fe/Ir(111) [10][11][12][13]. Furthermore, single magnetic skyrmions can be created as metastable excitations via the injection of currents [14][15][16], magnetic field pulses [17] and by tailored boundary conditions [18,19]. Depending on the involved magnetic interactions, magnetic skyrmions range in size from ∼ 1 µm in bulk systems to ∼ 1 nm at interfaces [2,10,13].…”

Regular and in-plane skyrmions and antiskyrmions from boundary instabilities

“…We consider a system with a boundary between regions of differing DMI and assume that the directions of the magnetic field and magnetic anisotropy do not change across the boundary. Using the variational principle, one can obtain the boundary conditions [20],…”

“…Due to different conditions required to create stable skyrmions or antiskyrmions, methods for their generation form an important piece of skyrmion related research. There are a number of theoretical proposals [18][19][20][21][22], as well as direct experimental observations of skyrmion generation [9,[23][24][25][26][27]. It is desirable to develop universal means for generating both skyrmions and antiskyrmions.…”

“…In the presence of edge or boundary instabilities, chiral domain walls can form from the twist of magnetization at the edge or boundary and evolve into skyrmions or antiskyrmions. Previous studies have investigated the possibility of skyrmion or antiskyrmion generation at edges or boundaries through application of magnetic field pulse [20,21]. Generation of skyrmions in the bulk by charge current pulses has also been proposed [36].…”

Crystalline Orientation–Dependent Spin Hall Effect in Epitaxial Platinum

“…The symmetries should be reflected in fundamental properties such as interfacial anisotropy (both in-plane and out-of-plane) [37] and Dzyaloshinskii-Moriya interaction (DMI) [38,39]. For low-symmetry systems such as Pt (220) with C 2v , the strength of the DMI may vary in magnitude or sign along different directions [40][41][42][43][44]. Such anisotropic DMI and anisotropy can stabilize novel phases such as antiskyrmions [41].…”