In cubic noncentrosymmetric ferromagnets uniaxial distortions suppress the helical states and stabilize Skyrmion lattices in a broad range of thermodynamical parameters. Using a phenomenological theory for modulated and localized states in chiral magnets, the equilibrium parameters of the Skyrmion and helical states are derived as functions of the applied magnetic field and induced uniaxial anisotropy.These results show that due to a combined effect of induced uniaxial anisotropy and an applied magnetic field Skyrmion lattices can be formed as thermodynamically stable states in large intervals of magnetic field and temperatures in cubic helimagnets, e.g., in intermetallic compounds MnSi, FeGe, (Fe,Co) where L is a vector order parameter (e.g. the magnetization vector M in magnetic materials or the director n in chiral liquid crystals), ∂ k L i ≡ ∂L i /∂x k are spatial derivatives of the order parameter. In condensed matter physics there are no physical interactions underlying energy contributions with higherorder spatial derivatives. [7] On the contrary, the invariants of type (1) arise in systems with intrinsic [9, 10] and induced chirality.[6] Particularly, in noncentrosymmetric magnetic materials such interactions stem from the chiral part of spin-orbit couplings (Dzyaloshinskii-Moriya interactions).[9] Chiral interactions of type (1) stabilize helical [9,11] and Skyrmionic structures [5,12] with fixed rotation sense (Fig. 1) [15]. Therefore, additional effects are necessary to stabilize Skyrmionic states in these systems. [2,13] In this paper we demonstrate that uniaxial distortions suppress the helical phases and enable the thermodynamic stability of the Skyrmion lattice in a broad range of applied magnetic fields. The calculated magnetic phase diagram allows to formulate practical recommendations on the possibility to stabilize Skyrmion states at low temperatures in MnSi, FeGe, (Fe,Co)Si and similar intermetallic compounds with B20-structure.Following the phenomenological theory developed in Refs. [9,11] we write the magnetic energy density for a cubic helimagnet with uniaxial distortions along z-axis aswhere A is the exchange stiffness, the second term is the Zeeman energy,zy ) =D M·rotM is the chiral energy with the Dzyaloshinskii constant D,i ] includes exchange (B) and cubic (K c ) anistropies [11]. The last term in (2) is uniaxial anisotropy induced by distortions.The Dzyaloshinskii-Moriya energy w D (2) favours spatially modulated chiral states where the magnetization rotates with a fixed turning sense in the plane perpendicular to the propagation direction (Fig. 1). The sign and magnitude of the Dzyaloshinskii constant D determine the modulation period and the sense of rotation, respectively. Thus, in zero magnetic field, H = 0, and for zero anisotropies, B = K c = K = 0, a flat helix forms the magnetic ground state as a single harmonic mode with wave number q 0 = D/(2A), where the phase angle φ of the magnetization varies linearly along the

This paper reports on magnetometry and magnetoresistance measurements of MnSi epilayers performed in out-of-plane magnetic fields. We present a theoretical analysis of the chiral modulations that arise in confined cubic helimagnets where the uniaxial anisotropy axis and magnetic field are both out-of-plane. In contrast to in-plane field measurements (Wilson et al., Phys. Rev. B 86, 144420 (2012)), the hard-axis uniaxial anisotropy in MnSi/Si(111) increases the energy of (111)oriented skyrmions and in-plane helicoids relative to the cone phase, and makes the cone phase the only stable magnetic texture below the saturation field. While induced uniaxial anisotropy is important in stabilizing skyrmion lattices and helicoids in other confined cubic helimagnets, the particular anisotropy in MnSi/Si(111) entirely suppresses these states in an out-of-plane magnetic field. However, it is predicted that isolated skyrmions with enlarged sizes exist in MnSi/Si(111) epilayers in a broad range of out-of-plane magnetic fields. These results reveal the importance of the symmetry of the anisotropies in bulk and confined cubic helimagnets in the formation of chiral modulations and they provide additional evidence of the physical nature of the A-phase states in other B20-compounds. 75.70.Ak

A detailed investigation of the magnetization processes in epitaxial MnSi thin film reveals the existence of elliptically distorted skyrmion strings that lie in the plane of the film. We provide proof that the uniaxial anisotropy stabilizes this state over extended regions of the magnetic phase diagram. Theoretical analysis of an observed cascade of first-order phase transitions is based on rig- orous numerical calculations of competing chiral modulations, which shows the existence of helicoids, elliptic skyrmions, and cone phases

Vortex states in magnetic nanodisks are essentially affected by surface/interface induced Dzyaloshinskii-Moriya interactions. Within a micromagnetic approach we calculate the equilibrium sizes and shape of the vortices as functions of magnetic field, the material and geometrical parameters of nanodisks. It was found that the Dzyaloshinskii-Moriya coupling can considerably increase sizes of vortices with "right" chirality and suppress vortices with opposite chirality. This allows to form a bistable system of homochiral vortices as a basic element for storage applications.

The magnetization process of antiferromagnetically coupled ͓͑Co/ Pt͒ 8 / Co/ Ru͔ 18 multilayers with perpendicular anisotropy is investigated via magnetic force microscopy at room temperature by imaging the domain configuration in magnetic fields. In the zero-field state, due to the perpendicular anisotropy, stripe domains characteristic for ferromagnetic coupling are observed. By increasing the external magnetic field, the domain configuration first modifies gradually, then transforms from continuous into isolated stripes, and changes in the end into bubbles, which collapse at higher fields. A theoretical model previously developed for bubble domains in single layer films is adapted for arbitrary complex multilayers and applied to the present layer architecture. The calculated values for strip-out and collapse fields compare well with the experimental results and demonstrate the validity of the theoretical description.

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Abstract. Structural defects in magnetic crystalline materials may locally change magnetic properties and can significantly influence the behavior of magnetic nanostructures. E.g., surface-induced Dzyaloshinskii-Moriya interactions can strongly affect vortex structures in magnetic nanodisks causing a chirality selection. Near lattice defects, the spin-orbit interactions induce local antisymmetric Dzyaloshinskii-Moriya exchange and cause effective anisotropies, which can result in spin canting. Broken inversion symmetry near a defect leads to locally chiral exchange. We present a phenomenological approach for dislocation-induced Dzyaloshinskii-Moriya couplings.As an example we investigate effects of a screw dislocation at the center of a magnetic nanodisk with a vortex state. By numerical calculations on vortex profiles we analyze equilibrium parameters of the vortex as functions of applied magnetic field and the material and geometrical parameters. It is proposed that magnetic nanodisks with defects provide a suitable experimental setting to study induced chirality by spin-orbit effects.