Topological magnon band structure of emergent Landau levels in a skyrmion lattice.

The motion of a spin excitation across topologically nontrivial magnetic order exhibits a deflection that is analogous to the effect of the Lorentz force on an electrically charged particle in an orbital magnetic field. We used polarized inelastic neutron scattering to investigate the propagation of magnons (i.e., bosonic collective spin excitations) in a lattice of skyrmion tubes in manganese silicide. For wave vectors perpendicular to the skyrmion tubes, the magnon spectra are consistent with the formation of finely spaced emergent Landau levels that are characteristic of the fictitious magnetic field used to account for the nontrivial topological winding of the skyrmion lattice. This provides evidence of a topological magnon band structure in reciprocal space, which is borne out of the nontrivial real-space topology of a magnetic order.

THE MEDICAL REFORM: REALITIES AND PROSPECTS FOR UKRAINE.

OBJECTIVE: The aim: is to analyze the realities and to determine prospects of the medical reform in Ukraine as a method of public administration of healthcare. PATIENTS AND METHODS: Materials and methods: The given paper uses an integrated approach, which consists in the study of public administration of healthcare as a single whole with the coordinated functioning of all its constituents; besides this, the methods, which were used at the empirical and theoretical levels, such as, an abstract logical method, a method of analyses and synthesis, and a method of comparison were applied in the given research. CONCLUSION: Conclusions: The medical reform is not a goal in itself, but when implementing the reform, it is necessary to consider other related processes, such as globalization, technological progress, urbanization, demographic crisis, macro-economic situation, unfinished distribution of the rights of property in business, specialization. Now, there is «The Strategy of the Reformation of Healthcare of Ukraine¼. And the proper use of the complex of methods of public administration, directed both at balanced growth of the national health field, and prevention of negative influence of related sectors and fields of national economy guarantees its successful realization.

Response of the Skyrmion Lattice in MnSi to Cubic Magnetocrystalline Anisotropies.

We report high-precision small-angle neutron scattering of the orientation of the Skyrmion lattice in a spherical sample of MnSi under systematic changes of the magnetic field direction. For all field directions the Skyrmion lattice may be accurately described as a triple-Q[over →] state, where the modulus |Q[over →]| is constant and the wave vectors enclose rigid angles of 120°. Along a great circle across ⟨100⟩, ⟨110⟩, and ⟨111⟩ the normal to the Skyrmion-lattice plane varies systematically by ±3° with respect to the field direction, while the in-plane alignment displays a reorientation by 15° for magnetic field along ⟨100⟩. Our observations are qualitatively and quantitatively in excellent agreement with an effective potential, which is determined by the symmetries of the tetrahedral point group T and includes contributions up to sixth order in spin-orbit coupling, providing a full account of the effect of cubic magnetocrystalline anisotropies on the Skyrmion lattice in MnSi.

Band Structure of Helimagnons in MnSi Resolved by Inelastic Neutron Scattering.

A magnetic helix realizes a one-dimensional magnetic crystal with a period given by the pitch length λh. Its spin-wave excitations-the helimagnons-experience Bragg scattering off this periodicity, leading to gaps in the spectrum that inhibit their propagation along the pitch direction. Using high-resolution inelastic neutron scattering, the resulting band structure of helimagnons was resolved by preparing a single crystal of MnSi in a single magnetic-helix domain. At least five helimagnon bands could be identified that cover the crossover from flat bands at low energies with helimagnons basically localized along the pitch direction to dispersing bands at higher energies. In the low-energy limit, we find the helimagnon spectrum to be determined by a universal, parameter-free theory. Taking into account corrections to this low-energy theory, quantitative agreement is obtained in the entire energy range studied with the help of a single fitting parameter.

Uniaxial Pressure Dependence of Magnetic Order in MnSi.

We report comprehensive small angle neutron scattering measurements complemented by ac susceptibility data of the helical order, conical phase, and Skyrmion lattice phase (SLP) in MnSi under uniaxial pressures. For all crystallographic orientations uniaxial pressure favors the phase for which a spatial modulation of the magnetization is closest to the pressure axis. Uniaxial pressures as low as 1 kbar applied perpendicular to the magnetic field axis enhance the Skyrmion lattice phase substantially, whereas the Skyrmion lattice phase is suppressed for pressure parallel to the field. Taken together we present quantitative microscopic information on how strain couples to magnetic order in the chiral magnet MnSi.

Polyoxometalate-stabilized, water dispersible Fe2Pt magnetic nanoparticles.

Magnetic Fe2Pt core-shell nanoparticles with 2 nm cores were synthesized with a monolayer coating of silicotungstate Keggin clusters. The core-shell composition is substantiated by structural analysis performed using high-resolution scanning transmission electron microscopy (HR-STEM) and small angle X-ray scattering (SAXS) in a liquid suspension. The molecular metal oxide cluster shell introduces an enhanced dispersibility of the magnetic Fe-Pt core-shell nanoparticles in aqueous media and thereby opens up new routes to nanoparticle bio-functionalization, for example, using pre-functionalized polyoxometalates.

Long-range crystalline nature of the Skyrmion lattice in MnSi.

We report small angle neutron scattering of the Skyrmion lattice in MnSi using an experimental setup that minimizes the effects of demagnetizing fields and double scattering. Under these conditions, the Skyrmion lattice displays resolution-limited Gaussian rocking peaks that correspond to a magnetic correlation length in excess of several hundred micrometers. This is consistent with exceptionally well-defined long-range order. We further establish the existence of higher-order scattering, discriminating parasitic double scattering with Renninger scans. The field and temperature dependence of the higher-order scattering arises from an interference effect. It is characteristic for the long-range crystalline nature of the Skyrmion lattice as shown by simple mean-field calculations.

Spin transfer torques in MnSi at ultralow current densities.

Spin manipulation using electric currents is one of the most promising directions in the field of spintronics. We used neutron scattering to observe the influence of an electric current on the magnetic structure in a bulk material. In the skyrmion lattice of manganese silicon, where the spins form a lattice of magnetic vortices similar to the vortex lattice in type II superconductors, we observe the rotation of the diffraction pattern in response to currents that are over five orders of magnitude smaller than those typically applied in experimental studies on current-driven magnetization dynamics in nanostructures. We attribute our observations to an extremely efficient coupling of inhomogeneous spin currents to topologically stable knots in spin structures.

Skyrmion lattices in metallic and semiconducting B20 transition metal compounds.

High pressure studies in MnSi suggest the existence of a non-Fermi liquid state without quantum criticality. The observation of partial magnetic order in a small pocket of the pressure versus temperature phase diagram of MnSi has additionally inspired several proposals of complex spin textures in chiral magnets. We used neutron scattering to observe the formation of a two-dimensional lattice of skyrmion lines, a type of magnetic vortices, under applied magnetic fields in metallic and semiconducting B20 compounds. In strongly disordered systems the skyrmion lattice is hysteretic and extends over a large temperature range. Our study experimentally establishes magnetic materials lacking inversion symmetry as an arena for new forms of spin order composed of topologically stable spin textures.

Skyrmion lattice in a chiral magnet.

Skyrmions represent topologically stable field configurations with particle-like properties. We used neutron scattering to observe the spontaneous formation of a two-dimensional lattice of skyrmion lines, a type of magnetic vortex, in the chiral itinerant-electron magnet MnSi. The skyrmion lattice stabilizes at the border between paramagnetism and long-range helimagnetic order perpendicular to a small applied magnetic field regardless of the direction of the magnetic field relative to the atomic lattice. Our study experimentally establishes magnetic materials lacking inversion symmetry as an arena for new forms of crystalline order composed of topologically stable spin states.

Quantum order in the chiral magnet MnSi.

Systems lacking inversion symmetry, such as selected three-dimensional compounds, multilayers and surfaces support Dzyaloshinsky-Moriya (DM) spin-orbit interactions. In recent years DM interactions have attracted great interest, because they may stabilize magnetic structures with a unique chirality and non-trivial topology. The inherent coupling between the various properties provided by DM interactions is potentially relevant for a variety of applications including, for instance, multiferroic and spintronic devices. The, perhaps, most extensively studied material in which DM interactions are important is the cubic B20 compound MnSi. We review the magnetic field and pressure dependence of the magnetic properties of MnSi. At ambient pressure this material displays helical order. Under hydrostatic pressure a non-Fermi liquid state emerges, where a partial magnetic order, reminiscent of liquid crystals, is observed in a small pocket. Recent experiments strongly suggest that the non-Fermi liquid state is not due to quantum criticality. Instead it may be the signature of spin textures and spin excitations with a non-trivial topology.