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Crystal lattices with tetragonal or hexagonal structure often exhibit structural transitions in response to external stimuli.sup.1. Similar behaviour is anticipated for the lattice forms of topological spin textures, such as lattices composed of merons and antimerons or skyrmions and antiskyrmions (types of vortex related to the distribution of electron spins in a magnetic field), but has yet to be verified experimentally.sup.2,3. Here we report real-space observations of spin textures in a thin plate of the chiral-lattice magnet Co.sub.8Zn.sub.9Mn.sub.3, which exhibits in-plane magnetic anisotropy. The observations demonstrate the emergence of a two-dimensional square lattice of merons and antimerons from a helical state, and its transformation into a hexagonal lattice of skyrmions in the presence of a magnetic field at room temperature. Sequential observations with decreasing temperature reveal that the topologically protected skyrmions remain robust to changes in temperature, whereas the square lattice of merons and antimerons relaxes to non-topological in-plane spin helices, highlighting the different topological stabilities of merons, antimerons and skyrmions. Our results demonstrate the rich variety of topological spin textures and their lattice forms, and should stimulate further investigation of emergent electromagnetic properties.A magnetically induced two-dimensional square lattice of merons and antimerons is observed in real space, along with its transformation into a hexagonal lattice of skyrmions at room temperature., Author(s): X. Z. Yu [sup.1] , W. Koshibae [sup.1] , Y. Tokunaga [sup.2] , K. Shibata [sup.1] , Y. Taguchi [sup.1] , N. Nagaosa [sup.1] [sup.3] , Y. Tokura [sup.1] [...]

Co–Zn–Mn chiral cubic magnets display versatile magnetic skyrmion phases, including equilibrium phases stable far above and far below room temperature, and the facile creation of robust far‐from‐equilibrium skyrmion states. In this system, compositional disorder and magnetic frustration are key ingredients that have profound effects on the chiral magnetism. Reported here are studies of the magnetism in Co6.75Zn6.75Mn6.5 by magnetometry, small‐angle neutron scattering (SANS), magnetic diffuse neutron scattering and Lorentz transmission electron microscopy (LTEM). While features in magnetometry and LTEM often give standard indications for skyrmion formation, they are not readily observed from the measurements on this system. Instead, skyrmion lattice correlations are only revealed by SANS, and they are found to form an orientationally disordered structure in a minority fraction of the sample. The majority fraction of the sample always displays orientationally disordered helical spin correlations, which undergo further disordering along the radial direction on cooling below the critical temperature (Tc ≃ 102 K). The near‐complete suppression of the skyrmion phase, and the process of disordering on cooling, are attributed to competing magnetic interactions that dominate over the ferromagnetic interaction expected to favour chiral magnetism in this system. These competing interactions start to develop above Tc and become further enhanced towards low temperatures. The present observations of co‐existing and disordered magnetic correlations over multiple length scales are not unique to Co6.75Zn6.75Mn6.5 but are seemingly common to the family of Co–Zn–Mn compounds with finite Mn, and their accurate description presents a challenge for theoretical modelling. In addition, this study highlights a need for neutron instrumentation capable of the comprehensive measurement of magnetic correlations over expanded ranges of momentum transfer in such multiple‐length‐scale magnets. [ABSTRACT FROM AUTHOR]

Cuprous iodide (CuI) is an emerging wide-bandgap semiconductor of superior optical and transport properties. In particular, CuI shows high stability and large oscillator strength of free excitons that are of great advantage for optoelectronic applications. However, thin films of CuI reported so far have not been genuine single crystals, containing a sizable density of impurity and defect. Here, we demonstrate a dramatic improvement in the quality of CuI films grown by molecular beam epitaxy on a lattice-matched InAs substrate. The film is revealed to be in a single-crystal structure with high lattice coherence and an atomically flat surface. The low-temperature photoluminescence spectra exhibit extremely sharp emission from free excitons and much-suppressed emission from trapped states. The high-quality CuI films realized in the present study will not only facilitate the device application of CuI films but also provide unprecedented functionalities in halide semiconductors at the atomically sharp heterointerfaces. [ABSTRACT FROM AUTHOR]

The article offers information about the nanometer-scale skyrmions as prospective candidates for information bits in low–power consumption devices owing to their topological nature and controllability with low current density. It mentions the study on skyrmion dynamics in different classes of materials have exploited the topological Hall effect and current-driven fast motion of skyrmionic bubbles.

We show a growth of high-quality thin films of a wide bandgap semiconductor copper iodide (CuI) on Al2O3 substrates by molecular beam epitaxy. Employing a thin buffer layer deposited at a lower temperature (160 °C) prior to the main growth, the maximum growth temperature is elevated up to 240 °C, resulting in a significant improvement in the crystallinity as verified by sharp x-ray diffraction peaks as well as a step-and-terrace structure observed by atomic force microscopy. Optimum films show more intense free exciton emission in photoluminescence spectra than others, implying the suppression of defects. These results indicate that the fabrication process developed in this study is quite effective at realizing high-quality CuI thin films. [ABSTRACT FROM AUTHOR]

Polycrystalline Fe0.4Mn0.6 layers with the different thickness are deposited on 4-nm-thick single-crystalline Co2FeAl layers, which are grown on GaAs (001) substrates at room temperature by molecular-beam epitaxy. Both the exchange bias and the in-plane magnetic anisotropies of the bilayers are strongly dependent on the thickness of the Fe0.4Mn0.6 layer. The former is described using a granular level model. A modified Stoner-Wohlfarth model is used to explain the in-plane magnetic anisotropies observed at 5 K, while one possible reason for the magnetic anisotropies measured at 300 K is the complex interfacial magnetic properties proved by x-ray magnetic circular dichroism measurements. [ABSTRACT FROM AUTHOR]

A 100-nm-thick Fe50Pt50 film with high coercivity was fabricated by magnetron sputtering. On introducing a Cr top/bottom layer, the ordering temperature (Tor) of the film decreased considerably from 500 to 380 °C. On introducing both Cr top/bottom layer and a 0.2-nm-thick Cu interlayer, the Tor decreased even further to 340 °C. During the annealing process, the number of Cr atoms diffused into the Fe50Pt50 layer increased. This increased the Fe diffusivity, lowering the Tor in the process. The diffusion of the additive and the effects of annealing were verified by selected-area electron diffraction observations and by investigating the temperature dependence of the magnetization. The superlattice structure of the ordered Fe50Pt50 film containing Cr and Cu additives was confirmed by the transmission electronic microscopy. Because of the Cr and Cu additives, the average grain size in the ordered Fe50Pt50 film increased slightly; however, the coercivity of the ordered Fe50Pt50 film is improved considerably. [ABSTRACT FROM AUTHOR]

The quantum anomalous Hall effect (QAHE) is an exotic quantum phenomenon originating from dissipationless chiral channels at the sample edge. While the QAHE has been observed in magnetically doped topological insulators (TIs), exploiting the magnetic proximity effect on the TI surface from adjacent ferromagnetic layers may provide an alternative approach to the QAHE by opening an exchange gap with less disorder than that in the doped system. Nevertheless, the engineering of a favorable heterointerface that realizes the QAHE based on the magnetic proximity effect remains to be achieved. Here, we report on the observation of the QAHE in a proximity coupled system of a nonmagnetic TI and a ferromagnetic insulator (FMI). We have designed sandwich heterostructures of (Zn,Cr)Te/(Bi,Sb)2Te3/(Zn,Cr)Te that fulfills two prerequisites for the emergence of the QAHE: the formation of a sizable exchange gap at the TI surface state and the tuning of the Fermi energy into the exchange gap. The efficient proximity coupling in the all-telluride based heterostructure as demonstrated here will enable a realistic design of versatile tailor-made topological materials coupled with ferromagnetism, ferroelectricity, superconductivity, and so on. [ABSTRACT FROM AUTHOR]

The soft X‐ray emissions from the Earth's magnetosheath and cusp regions are simulated under different solar wind conditions, based on the PPMLR‐MHD code. The X‐ray images observed by a hypothetical telescope are presented, and the basic responses of the magnetopause and cusp regions are discernable in these images. From certain viewing geometries, the magnetopause position in the equatorial plane, as well as the latitudinal scales and azimuthal extent of cusp can be directly extracted from the X‐ray images. With these reconstructed positions, the issues we are able to analyze include but are not limited to the compression of magnetopause and widening of the cusp after an enhancement of solar wind flux, as well as the erosion of the magnetopause and equatorward motion of cusp after the southward turning of the interplanetary magnetic field. Hence, the X‐ray imaging is an appropriate technique to study the large‐scale motion of magnetopause and cusps in response to solar wind variations. Key Points: X‐ray images are estimated based on MHD simulations under different solar wind conditionsResponses of the magnetopause to solar wind changes are analyzed from X‐ray imagesResponses of the cusp to solar wind variations are presented via X‐ray images [ABSTRACT FROM AUTHOR]

Hydroponic experiments were conducted to investigate the influence of chromium (Cr) exposure on assimilation of N-labeled nitrate in rice ( Oryza sativa L. cv. XZX 45) seedlings. Results showed that exposure of young seedlings to both Cr compounds led to a linear decrease in relative growth rate, nitrate reductase (NR) activity and tissue N accumulation though responses differed between the two Cr variants, in which potassium chromate [Cr(VI)] caused more severe effects than chromium chloride [Cr(III)]. Analysis of subcellular distribution of Cr showed that Cr deposition in cell wall was the highest in tissues of rice seedlings exposed to Cr(III), whereas the largest deposition of Cr in the roots was associated with cytosol in the Cr(VI) treatments. Analysis of a partial correlation between tissue fractions of Cr, NR activity and N content revealed that depression of NR activity in plant materials of rice seedlings exposed to Cr(III) was mainly associated with a decrease in N accumulation, whereas inhibition of NR activity from exposure of plants to Cr(VI) was most likely due to the presence of Cr in cytosol. Information collected here indicated that mechanisms of transport, subcellular distribution and phytotoxicity of the two Cr compounds were different in rice seedlings. [ABSTRACT FROM AUTHOR]

We have investigated nanometric magnetic textures in thin (<150 nm) plates of Ru-doped bilayered manganites La1.2Sr1.8(Mn1-yRuy)2O7. Ru substitution for Mn site changes the magnetic anisotropy from in-plane to out-of-plane easy axis type without any significant change of global magnetic and crystal structures. The combination of conventional and Lorentz transmission electron microscopy observations confirms the emergence of magnetic bubbles and skyrmions in the absence of magnetic field. With the changing Ru concentration, systematic changes in the type of magnetic bubbles are observed. A tiny residual magnetic field also affects the generation and the type-change of magnetic bubbles. [ABSTRACT FROM AUTHOR]

Spontaneously emergent chirality is an issue of fundamental importance across the natural sciences. It has been argued that a unidirectional (chiral) rotation of a mechanical ratchet is forbidden in thermal equilibrium, but becomes possible in systems out of equilibrium. Here we report our finding that a topologically nontrivial spin texture known as a skyrmion-a particle-like object in which spins point in all directions to wrap a sphere-constitutes such a ratchet. By means of Lorentz transmission electron microscopy we show that micrometre-sized crystals of skyrmions in thin films of Cu2OSeO3 and MnSi exhibit a unidirectional rotation motion. Our numerical simulations based on a stochastic Landau-Lifshitz-Gilbert equation suggest that this rotation is driven solely by thermal fluctuations in the presence of a temperature gradient, whereas in thermal equilibrium it is forbidden by the Bohr-van Leeuwen theorem. We show that the rotational flow of magnons driven by the effective magnetic field of skyrmions gives rise to the skyrmion rotation, therefore suggesting that magnons can be used to control the motion of these spin textures. [ABSTRACT FROM AUTHOR]

Chirality-that is, left- or right-handedness-is an important concept in a broad range of scientific areas. In condensed matter, chirality is found not only in molecular or crystal forms, but also in magnetic structures. A magnetic skyrmion is a topologically stable spin vortex structure, as observed in chiral-lattice helimagnets, and is one example of such a structure. The spin swirling direction (skyrmion helicity) should be closely related to the underlying lattice chirality via the relativistic spin-orbit coupling. Here, we report on the correlation between skyrmion helicity and crystal chirality in alloys of helimagnets Mn1−xFexGe with varying compositions by Lorentz transmission electron microscopy and convergent-beam electron diffraction over a broad range of compositions (x = 0.3-1.0). The skyrmion lattice constant shows non-monotonous variation with composition x, with a divergent behaviour around x = 0.8, where the correlation between magnetic helicity and crystal chirality changes sign. This originates from continuous variation of the spin-orbit coupling strength and its sign reversal in the metallic alloys as a function of x. Controllable spin-orbit coupling may offer a promising way to tune skyrmion size and helicity. [ABSTRACT FROM AUTHOR]

We have investigated the structure and physical properties of single phase LaSrVMoO6 thin films grown by pulsed-laser deposition on (111) perovskite substrates. Despite the use of a mixed target, a high degree of ordering of V and Mo ions in the double perovskite structure has been observed using x-ray diffraction, reflection high-energy electron diffraction, and high-angle annular dark-field scanning transmission electron microscopy. Unlike previous reports, we find ferrimagnetic ordering of V and Mo spins at ∼25 K, with saturation magnetization ∼0.7 μB/formula unit. Furthermore, the films are highly metallic with resistivity ∼78 μΩ cm at 2 K. [ABSTRACT FROM AUTHOR]

By means of an electron diffraction technique, crystal-lattice modulations were investigated for a hexaferrite, Ba0.5Sr1.5Zn2Fe12O22, showing a helimagnetic order below TN=320 K. We observed a lattice modulation with a wave vector Q=(0,0,3δ) below TN. The value of δ varies between ~0.23 and 0.5 as a function of temperature and corresponds well to that of the magnetic modulation vector. By applying magnetic fields, Ba0.5Sr1.5Zn2Fe12O22 was found to exhibit successive changes in the lattice modulation, accompanied by the modifications of the helical magnetic order. We concluded that the observed lattice modulation is induced by the helical magnetic order via exchange magnetostriction. [ABSTRACT FROM AUTHOR]

The skyrmion, a vortex-like spin-swirling object, is anticipatedto play a vital role in quantum magneto-transport processes such as the quantum Hall and topological Hall effects. The existence of the magnetic skyrmion crystal (SkX) state was recently verified experimentally for MnSi and Fe0.5Co0.5Si by means of small-angle neutron scattering and Lorentz transmission electron microscopy. However, to enable the application of such a SkX for spintronic function, materials problems such as a low crystallization temperature and low stability of SkX have to be overcome. Here we report the formation of SkX close to room temperature in thin-films of the helimagnet FeGe. In addition to the magnetic twin structure, we found a magnetic chirality inversion of the SkX across lattice twin boundaries. Furthermore, for thin crystal plates with thicknesses much smaller than the SkX lattice constant (as) the two-dimensional SkX is quite stable over a wide range of temperatures and magnetic fields, whereas for quasi-three-dimensional films with thicknesses over as the SkX is relatively unstable and observed only around the helical transition temperature. The room-temperature stable SkX state as promised by this study will pave a new path to designing quantum-effect devices based on the controllable skyrmion dynamics. [ABSTRACT FROM AUTHOR]