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We present a systematic study of tilted spiral states obtained theoretically within the classical Dzyaloshinskii model for magnetic states in cubic non-centrosymmetric ferromagnets. Such tilted spirals are shown to stabilize under the competing effect of cubic and exchange anisotropies inherent to cubic helimagnets. By focusing on the internal structure of these spirals and their field-driven behaviour for different aspect ratios of the anisotropy coefficients, we are able to capture the main features of the experimental findings in a bulk cubic helimagnet Cu2OSeO3 and to make a step further towards a complete quantitative model of this chiral magnet. In particular, we show that for strong anisotropy values (which experimentally correspond to low temperatures near zero) there exist an angular separation between the conical and tilted spirals, i.e., the conical spiral flips into a tilted state and immediately composes some finite angle with respect to the field direction. As the anisotropy ratio decreases, such a transition between two spiral states becomes almost continuous and corresponds to higher temperatures at the experiments. In addition, we investigate the field-driven reorientation of metastable skyrmion lattices induced by the competing anisotropies, which may be responsible for some peculiarities at the experimental phase diagrams of Cu2OSeO3.

We study axially symmetrical 3D skyrmionic particles (torons, Hopfions) in a thin homeotropic cell filled with a cholesteric liquid crystal. We show that a small 3D skyrmion asymptotically can be presented as a particle with six multipole moments. In this case, the odd moments – dipole, octupole and the fifth-order moments – are helicoidal moments, generated by chirality. And even moments – quadrupole, hexadecapole and sixth order moments – have the usual form, as colloidal particles in nematics. Thus, we find the exact analytical solution for the far field director configuration around the 3D skyrmion and the exact analytical expression for the elastic interaction potential between 3D skyrmions in a homeotropic cell with thickness L. We show that it has an exponential decay length equal λ S S = L / π. The comparison with the experiment allows us to recover approximately one set of multipole coefficients for the small 3D skyrmion. We also describe the expansion of the skyrmion bag analytically depending on the number N of anti-skyrmions in it and obtain an agreement with the experiment. Along the way, we determined the director field and the elastic interaction potential betweenchiral axially symmetric colloidal particles in the unlimited nematic and in the homeotropic cell, taking into account higher order elastic terms. [ABSTRACT FROM AUTHOR]

Chiral spin textures have emerged as a captivating class of topological matter. These intriguing structures harbor localized and topologically protected magnetic textures, rendering them promising candidates for novel spintronic applications. Here, the emergent chiral spin textures in an iron garnet with nanodisk configuration have been micromagnatically simulated based on the Landau-Lifshitz-Gilbert equation (LLG) of COMSOL Multiphysics. The modification of magnetic spin texture in the considered iron garnet has been controlled by introducing the interfacial Dzyaloshinskii-Moriya interaction (I-DMI) and spin alignment constraints as locally pinned spins and curvilinear defects at edges. These boundary conditions induced interesting chiral textures not commonly observed in such iron garnet due to its centrosymmetric crystal structure. The simulation results showed the presence of two distinct regions of spin texture: inside and outside the pinning boundary. By systematically varying the DMI strength (D) with the size of the pinning boundary (R pin) and the number of defects (N def), the emerging chiral spin textures have been explored and reported, including the existence of ramified helical stripes, skyrmions, and skyrmions-like textures such as elongated skyrmions, chiral horseshoe domains, biskyrmions and target skyrmions (TSk) (2π-TSk and 3π-TSk). Also, it has been reported that various collapses occur in the final spin texture states, leading to the transition from one state to another when varying the values of R pin and N def with D. [ABSTRACT FROM AUTHOR]

The crystal structures of praseodymium silicide (5/4), Pr5Si4, and neodymium silicide (5/4), Nd5Si4, were redetermined using high-quality single-crystal X-ray diffraction data. The previous structure reports of Pr5Si4 were only based on powder X-ray diffraction data [Smith et al. (1967). Acta Cryst. 22 940–943; Yang et al. (2002b). J. Alloys Compd. 339, 189–194; Yang et al., (2003). J. Alloys Compd. 263, 146–153]. On the other hand, the structure of Nd5Si4 has been determined from powder data [neutron; Cadogan et al., (2002). J. Phys. Condens. Matter, 14, 7191–7200] and X-ray [Smith et al. (1967). Acta Cryst. 22 940–943; Yang et al. (2002b). J. Alloys Compd. 339, 189–194; Yang et al., (2003). J. Alloys Compd. 263, 146–153] and single-crystal data with isotropic atomic displacement parameters [Roger et al., (2006). J. Alloys Compd. 415, 73–84]. In addition, the anisotropic atomic displacement parameters for all atomic sites have been determined for the first time. These compounds are confirmed to have the tetragonal Zr5Si4-type structure (space group: P41212), as reported previously (Smith et al., 1967). The structure is built up by distorted body-centered cubes consisting of Pr(Nd) atoms, which are linked to each other by edge-sharing to form a three-dimensional framework. This framework delimits zigzag channels in which the silicon dimers are situated.

We develop a theory for the dynamics of a magnon on top of a domain wall in a ferromagnetic nanotube. Due to the geometry of the sample, domain walls are classified by the Skyrmion charge which counts the winding number of magnetic textures. The domain wall with a non-zero Skyrmion charge generates an emergent magnetic field for magnons, which exerts the Lorentz force on moving magnons and thereby deflects their trajectories. This deflection is manifested as the generation of the finite orbital angular momentum of the magnon that traverses the domain wall. We obtain exact solutions for the magnon on top of the Skyrmion-textured domain wall and also their scattering properties with the domain wall with the aid of supersymmetric quantum mechanics. We show that there is a critical wavenumber for the total reflection of magnons and it is discretized by the Skyrmion charge of the domain wall. Our results show that the orbital angular momenta of magnetic textures and magnons can be intertwined in a curved geometry.

Magnetic skyrmions are topologically nontrivial spin configurations that possess particle-like properties. Earlier research has mainly focused on a specific type of skyrmion with topological charge Q = -1. However, theoretical analyses of 2D chiral magnets have predicted the existence of skyrmion bags-solitons with arbitrary positive or negative topological charge. Although such spin textures are metastable states, recent experimental observations have confirmed the stability of isolated skyrmion bags in a limited range of applied magnetic fields. Here, by utilizing Lorentz transmission electron microscopy, the extraordinary stability of skyrmion bags in thin plates of B20-type FeGe is shown. In particular, it is shown that skyrmion bags embedded within a skyrmion lattice remain stable even in zero or inverted external magnetic fields. A robust protocol for nucleating such embedded skyrmion bags is provided. The results agree perfectly with micromagnetic simulations and establish thin plates of cubic chiral magnets as a powerful platform for exploring a broad spectrum of topological magnetic solitons., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Cr1/3TaS2—a candidate of chiral magnet—has been reported as a trivial ferromagnetic material. In contrast, the Cr1/3TaS2 single crystals exhibit a chiral helimagnetic (CHM) transition near 140 K. The magnetic moment versus magnetic field curves reveal a CHM—chiral soliton lattice (CSL)—forced ferromagnetic (FFM) transition in the magnetic ordered state. The conducting electrons interact with the CHM and CSL orders, giving rise to the nontrivial magnetoresistance (MR) in the Cr1/3TaS2 single crystals. The normalized magnetic moment and normalized MR fit well with the analytical functions for chiral soliton density. The magnetic phase diagrams constructed from the magnetic moment data and MR data suggest a possible tri‐critical point. Compared with the isostructural Cr1/3NbS2, the CHM transition temperature of Cr1/3TaS2 is 13 K higher, the CSL—FFM transition field is about 10 times larger, and the Dzyaloshinskii‐Moriya interaction strength is 3 times bigger. The latter two likely originate from the strong spin‐orbit coupling (SOC) of Cr1/3TaS2. The work clarifies that high‐quality Cr1/3TaS2 single crystals are chiral magnets and Cr1/3(Nb,Ta)S2 could serve as an intriguing platform for the flexible engineering of chiral magnetic solitons with tunable SOC. [ABSTRACT FROM AUTHOR]

The crystal structures of praseodymium silicide (5/4), Pr5Si4, and neodymium silicide (5/4), Nd5Si4, were redetermined using high-quality single-crystal X-ray diffraction data. The previous structure reports of Pr5 Si4 were only based on powder X-ray diffraction data [Smith et al. (1967). Acta Cryst. 22 940-943; Yang et al. (2002b). J. Alloys Compd. 339, 189-194; Yang et al., (2003). J. Alloys Compd. 263, 146-153]. On the other hand, the structure of Nd5Si4 has been determined from powder data [neutron; Cadogan et al., (2002). J. Phys. Condens. Matter, 14, 7191-7200] and X-ray [Smith et al. (1967). Acta Cryst. 22 940-943; Yang et al. (2002b). J. Alloys Compd. 339, 189-194; Yang et al., (2003). J. Alloys Compd. 263, 146-153] and single-crystal data with isotropic atomic displacement parameters [Roger et al., (2006). J. Alloys Compd. 415, 73-84]. In addition, the anisotropic atomic displacement parameters for all atomic sites have been determined for the first time. These compounds are confirmed to have the tetragonal Zr5 Si4 -type structure (space group: P41 212), as reported previously (Smith et al., 1967). The structure is built up by distorted bodycentered cubes consisting of Pr(Nd) atoms, which are linked to each other by edge-sharing to form a three-dimensional framework. This framework delimits zigzag channels in which the silicon dimers are situated. [ABSTRACT FROM AUTHOR]

Abstract Topological spin textures, such as magnetic skyrmions observed in certain chiral magnets, are one of the most interesting ordered phases in condensed matter. A skyrmion is a swirling spin structure carrying a topological quantum number. Skyrmions were first observed in MnSi, in 2009, and later observed in Cu 2 OSeO 3 , a chiral antiferromagnet with T N = 58 K that can be synthesized by reacting CuO and SeO 2 at 600 ° C. Using a transport agent (typically ammonium chloride) in a chemical vapour transport reaction, single crystals can be grown. As skyrmion lattices may find use in nanotechnological devices, such as data storage systems and in other applications, the magnetic properties of nano-sized compounds deserve to be investigated. The following work presents the synthesis and magnetic studies of the nanocrystalline form of Cu 2 OSeO 3 obtained by an alternative route, thermal decomposition of CuSeO 3 ·2 H 2 O. This procedure afforded nanostructured samples of reasonable purity (> 95 %). Structural, morphological and magnetic characterization of these samples are reported, aiming to study the effect of nanostructuring on the magnetic phases, in particular the presence and stability of the skyrmionic lattice. [ABSTRACT FROM AUTHOR]

The electronic state and the structural properties of the helical magneto-electric material Cu 2 OSeO 3 is investigated through temperature-dependent synchrotron based x-ray diffraction and x-ray absorption spectroscopy. The x-ray absorption spectra on Cu and Se- K edges indicate that Cu and Se ions are in the 2＋ and 4＋ charge states respectively. The pre-edge corresponding to K -line of Cu in the x-ray absorption spectra cannot be fitted using a single Lorentzian function. At least two different Lorentzian lines are required to fit the pre-edge, which are separated by ∼ 0. 6 ± 0. 042 eV. This separation originates due to the difference in the crystallographic environment of Cu(1) and Cu(2) and the subsequent difference in the energy of the 3 d orbitals of two Cu sites. The obtained energy difference reconfirms the value reported using resonant inelastic x-ray scattering and maximally localized Wannier function calculation. The synchrotron based powder x-ray diffraction indicates significant anomaly in the Cu-O-Cu bond angle around the magnetic transition temperature ( T C ∼ 59 K). Interestingly, the sample show negative thermal expansion in the lattice parameter below T C. Such anomalies can be connected to the exchange-striction mechanism. • Anomalous structural variation in a helical magneto-electric material Cu 2 OSeO 3. • Presence of exchange striction at the magnetic transition. • X-ray absorption spectroscopy indicates ＋2 and ＋4 ionic states of Cu and Se, respectively. • Multiple peak structure of the pre edge of x-ray absorption spectroscopy data corroborating two inequivalent positions of Cu. [ABSTRACT FROM AUTHOR]

Target skyrmion, characterized by a central skyrmion surrounded by a series of concentric cylinder domains known as kπ- skyrmions ( k ≥ 2), holds promise as a novel storage state in next-generation memories. However, target skyrmions comprising one or more concentric cylindrical domains have not been observed in chiral magnets, particularly at room temperature. In this study, we experimentally achieved kπ- skyrmions ( k = 2, 3, and 4) with diameters of ∼220, 320, and 410 nm, respectively, and room-temperature stability under zero magnetic field by tightly confining these topological spin textures in β-Mn-type Co 8 Zn 10 Mn 2 nanodisks. The magnetic configurations and their field-driven evolutions were simultaneously investigated by using in situ off-axis electron holography. In combination with numerical simulations, we further investigated the dependence of k max on the nanodisk diameter. These findings highlight the potential of k π-skyrmions as information carriers and offer insights into manipulation of k π-skyrmions in the future.

Graphical abstract By changing the terminal coordination atoms, chiral magnet HPU-12 was obtained. The magnetic measurements show the presence of antiferromagnetic interactions between the magnetic centers of the two complexes. Abstract The solvothermal reaction of (HL = 2-(5-Pyrazinyl-1H-[1,2,4]triazol-3-yl)-pyrazine) and NiCl 2 ·6H 2 O and Mn(HCOO) 2 ·2H 2 O yielded two novel complexes, namely, Ni(L)(Cl)(DMF) (HPU-11) and {Mn(L)(HCOO)} n (HPU-12), which have been studied based on X-ray single crystal diffraction analysis. In HPU-11 , two crystallographic independent NiII ions are connected by two L− ligands to generate a centrosymmetric binuclear cluster. By changing the terminal coordination atom Cl as HCOO, chiral magnet HPU-12 was obtained. In HPU-12 , adjacent Mn ions are connected by HCOO− bridges giving rise to a one-dimensional chiral chain structure. The magnetic measurements show the presence of antiferromagnetic interactions between the magnetic centers of the two complexes. [ABSTRACT FROM AUTHOR]

The compass-type anisotropy appears naturally in chiral magnets with strong spin-orbit coupling. In this work, we investigate the critical roles of compass anisotropy in modulating various spin textures of chiral magnets, by Monte Carlo simulations. The simulated results reveal a gradual helical reorientation and varying symmetry of skyrmion crystal structures as a function of compass anisotropy. Furthermore, an extended continuum spin model with the lattice discretization anisotropy is proposed to interpret the dependences of helical and skyrmion crystal structures on the compass anisotropy. It is demonstrated that specific helical propagating directions are favored by the high-order lattice anisotropy arising from spin interactions in discretized lattice. Besides that, some threshold values for the helical structures are identified by analytical approach. [ABSTRACT FROM AUTHOR]

To utilize magnetic skyrmions, nanoscale vortex-like magnetic structures, experimental elucidation of their dynamics against current application in various circumstances such as in confined structure and mixture of different magnetic phases is indispensable. Here, we investigate the current-induced dynamics of the coexistence state of magnetic skyrmions and helical magnetic structure in a thin plate of B20-type helimagnet FeGe in terms of in situ real-space observation using Lorentz transmission electron microscopy. Current pulses with various heights and widths were applied, and the change of the magnetic domain distribution was analyzed using a machine-learning technique. The observed average driving direction of the two-magnetic-state domain boundary is opposite to the applied electric current, indicating ferromagnetic s-d exchange coupling in the spin-transfer torque mechanism. The evaluated driving distance tends to increase with increasing the pulse duration time, current density (>1 × 109 A/m²), and sample temperature, providing valuable information about hitherto unknown current-induced dynamics of the skyrmion-lattice ensemble. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions in Co8Zn8Mn4 thin plates are observed to deform in a metastable state prepared in a magnetic-field-cooling process by way of the thermal-equilibrium skyrmion phase. In cooling, the disk-shape skyrmions change to bar- or L-shaped elongated form, whereas the skyrmion density is nearly conserved. The deformation of the skyrmions in the supercooled metastable phase is observed irrespective of the crystallographic orientation of the thin plate, whereas the elongation direction nearly aligns along the magnetic easy axis. It is proposed that the deformation should be induced by a large increase in magnetic modulation wavenumber when decreasing the temperature, whereas the topological protection of the skyrmions keeps the averaged skyrmion density constant. [ABSTRACT FROM AUTHOR]

The interfacial Dzyaloshinskii-Moriya interaction (DMI) is intimately related to the prospect of superior domain-wall dynamics and the formation of magnetic skyrmions. Although some experimental efforts have been recently proposed to quantify these interactions and the underlying physics, it is still far from trivial to address the interfacial DMI. Inspired by the reported tilt of the magnetization of the side edge of a thin film structure, we here present a quasi-static, straightforward measurement tool. By using laterally asymmetric triangular-shaped microstructures, it is demonstrated that interfacial DMI combined with an in-plane magnetic field yields a unique and significant shift in magnetic hysteresis. By systematic variation of the shape of the triangular objects combined with a droplet model for domain nucleation, a robust value for the strength and sign of interfacial DMI is obtained. This method gives immediate and quantitative access to DMI, enabling a much faster exploration of new DMI systems for future nanotechnology. [ABSTRACT FROM AUTHOR]

Monoaxial chiral magnets can form a noncollinear twisted spin structure called the chiral helimagnetic state. We study magnetic properties of such a chiral helimagnetic state, with emphasis on the effect of itinerant electrons. Modeling a monoaxial chiral helimagnet by a one-dimensional Kondo lattice model with the Dzyaloshinskii–Moriya interaction, we perform a variational calculation to elucidate the stable spin configuration in the ground state. We obtain a chiral helimagnetic state as a candidate for the ground state, whose helical pitch is modulated by the model parameters: the Kondo coupling, the Dzyaloshinski–Moriya interaction, and electron filling. [ABSTRACT FROM AUTHOR]

Dzyaloshinskii-Moriya interaction (DMI), which arises from the broken inversion symmetry and spin-orbit coupling, is of prime interest as it leads to a stabilization of chiral magnetic order and provides an efficient manipulation of magnetic nanostructures. Here, we report all-electrical measurement of DMI using propagating spin wave spectroscopy based on the collective spin wave with a well-defined wave vector. We observe a substantial frequency shift of spin waves depending on the spin chirality in Pt/Co/MgO structures. After subtracting the contribution from other sources to the frequency shift, it is possible to quantify the DMI energy in Pt/Co/MgO systems. The result reveals that the DMI in Pt/Co/MgO originates from the interfaces, and the sign of DMI corresponds to the inversion asymmetry of the film structures. The electrical excitation and detection of spin waves and the influence of interfacial DMI on the collective spin-wave dynamics will pave the way to the emerging field of spin-wave logic devices. [ABSTRACT FROM AUTHOR]

We investigate a role of impurity doping on the formation of a spiral structure in a chiral magnet. Our calculations are based on classical Monte Carlo technique and incorporate exchange and Dzyaloshinskii–Moriya interaction in terms of effective localized spins. As an application of our model we consider Co doping in a compound Fe 1 − x Co x Si. We reveal that adding impurity changes chiral fluctuations, leads to a decrease of the spiral wave vector which completely vanishes at a critical impurity concentrations. We analyze the behavior of the Bragg intensity profile as a function of doping. At an intermediate impurity concentrations we observe a disordered structure characterized by a Bragg spot around q = 0 in the q -space. • The dependence of the spiral structure in helimagnets on impurity doping is investigated. • The change of chirality upon doping is confirmed. • Model of localized spins for impurities is explored. [ABSTRACT FROM AUTHOR]

The formation of topological spin textures at the nanoscale has a significant impact on the long-range order and dynamical response of magnetic materials. We study the relaxation mechanisms at the conical-to-helical phase transition in the chiral magnet FeGe. By combining macroscopic ac susceptibility measurement, surface-sensitive magnetic force microscopy, and micromagnetic simulations, we demonstrate how the motion of magnetic topological defects, here edge dislocations, impacts the local formation of a stable helimagnetic spin structure. Although the simulations show that the edge dislocations can move with a velocity up to 100 m/s through the helimagnetic background, their dynamics are observed to disturb the magnetic order on the time scale of minutes due to randomly distributed pinning sites. The results corroborate the substantial impact of dislocation motions on the nanoscale spin structure in chiral magnets, revealing previously hidden effects on the formation of helimagnetic domains and domain walls.

Abstract: Interplay of crystallographic chirality and magnetic chirality has been of great interest in both chemist''s and physicist''s viewpoints. Crystals belonging to chiral space groups are eligible to stabilize macroscopic chiral magnetic order. This class of magnetic order is described by the chiral XY model, where the transverse magnetic field perpendicular to the chiral axis causes the chiral soliton lattice (CSL) formation. As a clear evidence of the chiral magnetic order, the temperature dependence of the transverse magnetization exhibits sharp cusp just below the mean field ferrimagnetic transition temperature, indicating the formation of the CSL. In addition to the static anomaly, we expect the CSL formation also causes dynamical anomalies such as induction of the spin supercurrent. [Copyright &y& Elsevier]

Exotic topological spin textures such as emergent magnetic monopole/anti-monopoles (hedgehog/anti-hedgehog) in the metastable extended skyrmion-strings attract much attention to the fundamental physics owing to their novel electromagnetic properties. However, the direct imaging of such spin textures is lacking. Here, we report the real-space observation of emergent magnetic monopoles involved in extended skyrmion-strings by Lorentz transmission electron microscopy (TEM) in combination with micromagnetic simulations. The in-plane extended skyrmion-strings are observed directly by Lorentz TEM to accompany the topological hedgehog-like defect, where the skyrmion-string terminates or merges with another skyrmion-string, as well as the surface-related defects where skyrmion-string bends 90° and ends on the surface. We also demonstrate the transformation of a metastabilized lattice of out-of-plane short skyrmion-strings into an in-plane array of extended skyrmion-strings by tuning the magnitude of oblique fields in a room-temperature helimagnet, revealing the stability of such topological spin textures and the possibility to control them.

Magnetic structures in magnetic artificial lattices and chiral magnetic orders in chiral magnets have been quantitatively analyzed in the reciprocal space by means of small-angle electron scattering (SAES) method. Lorentz deflection due to magnetic moments and Bragg diffraction due to periodicity are simultaneously recorded at an angle of the order of or less than 1 × 10−6 rad, using a camera length of more than 100 m. The present SAES method, together with TEM real-space imaging methods such as in-situ Lorentz microscopy, is very powerful in analyzing magnetic fine structures in magnetic materials. Indeed, the existence of both a chiral helimagnetic structure and a chiral magnetic soliton lattice in a chiral magnet CrNb3S6 has been successfully verified for the first time using the present complementary methods. [ABSTRACT FROM PUBLISHER]

Abstract: Thermodynamic nature of the magnetic transitions of a cyano-bridged WV–CuII compound of [W(CN)8]4[Cu(pn)H2O]4[Cu(pn)]2·2.5H2O is studied by low-temperature heat capacity measurements. Distinct thermal anomalies were observed in the temperature dependence of the heat capacity at 7.8K for chiral compound (S-enantiomer) and 7.2K for racemic compound. They are associated with the antiferromagnetic transitions reported by the previous magnetization measurements. In the case of S-enantiomer, a shoulder structure of Cp /T has been observed just below the main peak of the antiferromagnetic transition temperature at 0T. The shoulder grows to a sharp anomaly with a first order character by applying magnetic field of about 1T in the b-axis direction. On the other hand, just a broadening of the peak was observed for racemic compound, which means that the complicated behavior under magnetic field is derived from the crystallographic chirality. We also studied the behavior of S-enantiomer with magnetic fields applied parallel to the c-axis and found that the first order transition is not induced. Appearance of the complicated peak structure including the first order character specific in the b-direction is ascribed to peculiar magnetic ordering derived from crystallographic chirality related to the Dzyaloshinskii–Moriya (DM) interaction. [Copyright &y& Elsevier]