Magnetic Unit Research Articles

Thermodynamically stable skyrmion lattice in a tetragonal frustrated antiferromagnet with dipolar interaction

Motivated by recent experimental results on GdRu$_2$Si$_2$ [Khanh, N.D., Nakajima, T., Yu, X. et al., \emph{Nat. Nanotechnol.} \textbf{15}, 444-449 (2020)], where nanometric square skyrmion lattice was observed, we propose simple analytical mean-field description of the high-temperature part of the phase diagram of centrosymmetric tetragonal frustrated antiferromagnets with dipolar interaction in the external magnetic field. In the reciprocal space dipolar forces provide momentum dependent biaxial anisotropy. It is shown that in tetragonal lattice in the large part of the Brillouin zone for mutually perpendicular modulation vectors in the $ab$ plane this anisotropy has mutually perpendicular easy axes and collinear middle axes, what leads to double-Q modulated spin structure stabilization. The latter turns out to be a square skyrmion lattice in the large part of its stability region with the topological charge $\pm 1$ per magnetic unit cell, which is determined by the frustrated exchange coupling, and, thus, nanometer-sized. In the presence of additional single-ion easy-axis anisotropy, easy and middle axes can be swapped, which leads to different phase diagram. It is argued that the latter case is relevant to GdRu$_2$Si$_2$.

Encoding Information on the Excited State of a Molecular Spin Chain

AbstractThe quantum states of nano‐objects can drive electrical transport properties across lateral and local‐probe junctions. This raises the prospect, in a solid‐state device, of electrically encoding information at the quantum level using spin‐flip excitations between electron spins. However, this electronic state has no defined magnetic orientation and is short‐lived. Using a novel vertical nanojunction process, these limitations are overcome and this steady‐state capability is experimentally demonstrated in solid‐state spintronic devices. The excited quantum state of a spin chain formed by Co phthalocyanine molecules coupled to a ferromagnetic electrode constitutes a distinct magnetic unit endowed with a coercive field. This generates a specific steady‐state magnetoresistance trace that is tied to the spin‐flip conductance channel, and is opposite in sign to the ground state magnetoresistance term, as expected from spin excitation transition rules. The experimental 5.9 meV thermal energy barrier between the ground and excited spin states is confirmed by density functional theory, in line with macrospin phenomenological modeling of magnetotransport results. This low‐voltage control over a spin chain's quantum state and spintronic contribution lay a path for transmitting spin wave‐encoded information across molecular layers in devices. It should also stimulate quantum prospects for the antiferromagnetic spintronics and oxides electronics communities.

Emergent Magnetic Phases in Pressure-Tuned van der Waals Antiferromagnet FePS3

Layered van der Waals 2D magnetic materials are of great interest in fundamental condensed-matter physics research, as well as for potential applications in spintronics and device physics. We present neutron powder diffraction data using new ultrahigh-pressure techniques to measure the magnetic structure of Mott-insulating 2D honeycomb antiferromagnet FePS3 at pressures up to 183 kbar and temperatures down to 80 K. These data are complemented by high-pressure magnetometry and reverse Monte Carlo modeling of the spin configurations. As pressure is applied, the previously measured ambient-pressure magnetic order switches from an antiferromagnetic to a ferromagnetic interplanar interaction and from 2D-like to 3D-like character. The overall antiferromagnetic structure within the ab planes, ferromagnetic chains antiferromagnetically coupled, is preserved, but the magnetic propagation vector is altered from k=(0,1,12) to k=(0,1,0), a halving of the magnetic unit cell size. At higher pressures, coincident with the second structural transition and the insulator-metal transition in this compound, we observe a suppression of this long-range order and emergence of a form of magnetic short-range order which survives above room temperature. Reverse Monte Carlo fitting suggests this phase to be a short-ranged version of the original ambient-pressure structure—with the Fe moment size remaining of similar magnitude and with a return to antiferromagnetic interplanar correlations. The persistence of magnetism well into the HP-II metallic state is an observation in contradiction with previous x-ray spectroscopy results which suggest a spin-crossover transition.1 MoreReceived 9 April 2020Revised 15 September 2020Accepted 28 October 2020DOI:https://doi.org/10.1103/PhysRevX.11.011024Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasMagnetic orderMagnetic phase transitionsMagnetismQuantum phase transitionsPhysical Systems2-dimensional systemsAntiferromagnetsHoneycomb latticeMagnetic systemsMott insulatorsStrongly correlated systemsTechniquesMagnetic techniquesMethods in magnetismNeutron diffractionNeutron techniquesSusceptibility measurementsCondensed Matter, Materials & Applied Physics

Destruction of long-range magnetic order in an external magnetic field and the associated spin dynamics in Cu2GaBO5 and Cu2AlBO5 ludwigites

The quantum spin systems Cu$_2$M'BO$_5$ (M' = Al, Ga) with the ludwigite crystal structure consist of a structurally ordered Cu$^{2+}$ sublattice in the form of three-leg ladders, interpenetrated by a structurally disordered sublattice with a statistically random site occupation by magnetic Cu$^{2+}$ and nonmagnetic Ga$^{3+}$ or Al$^{3+}$ ions. A microscopic analysis based on density-functional-theory calculations for Cu$_2$GaBO$_5$ reveals a frustrated quasi-two-dimensional spin model featuring five inequivalent antiferromagnetic exchanges. A broad low-temperature $^{11}$B nuclear magnetic resonance points to a considerable spin disorder in the system. In zero magnetic field, antiferromagnetic order sets in below $T_\text{N}$ $\approx$ 4.1 K and ~2.4 K for the Ga and Al compounds, respectively. From neutron diffraction, we find that the magnetic propagation vector in Cu$_2$GaBO$_5$ is commensurate and lies on the Brillouin-zone boundary in the (H0L) plane, $\mathbf{q}_\text{m}$ = (0.45 0 -0.7), corresponding to a complex noncollinear long-range ordered structure with a large magnetic unit cell. Muon spin relaxation is monotonic, consisting of a fast static component typical for complex noncollinear spin systems and a slow dynamic component originating from the relaxation on low-energy spin fluctuations. Gapless spin dynamics in the form of a diffuse quasielastic peak is also evidenced by inelastic neutron scattering. Most remarkably, application of a magnetic field above 1 T destroys the static long-range order, which is manifested in the gradual broadening of the magnetic Bragg peaks. We argue that such a crossover from a magnetically long-range ordered state to a spin-glass regime may result from orphan spins on the structurally disordered magnetic sublattice, which are polarized in magnetic field and thus act as a tuning knob for field-controlled magnetic disorder.

ТЕХНОЛОГИЯ МАГНИТНОЙ ОБРАБОТКИ ВОДЫ ПРОТИВ СОЛЕОТЛОЖЕНИЯ: ТЕОРИЯ И ПРАКТИКА

Актуальность исследования определяется широким применением водных георесурсов в качестве рабочих тел в гидро- и теплоэнергетике, в системах теплоснабжения и охлаждения. При этом часто требуется произвести технологическую водоподготовку перед выполнением основного производственного цикла. В частности,воду требуется очищать от коллоидных, накипеобразующих и газообразных примесей. Наибольшую сложность представляет очистка воды от солей жесткости, то есть ее умягчение. Соли кальция и магния обычно выпадают на поверхностях теплообмена с образованием накипи, что приводит к резкому снижению эффективности работы теплообменного оборудования, перерасходу топлива и частым остановкам для чистки. Удаляют накипь обычно путем кислотных промывок внутренних поверхностей теплообмена или механическим способом. Все эти методы связаны с применением большого количества химических реагентов и сильно загрязняют сточные воды.Кроме того, это значительно увеличивает эксплуатационные расходы. Цель настоящего исследования заключается в теоретическом описании электрохимических процессов, происходящих в установках с постоянными тороидальными магнитами, при пропускании потока воды с растворенными в ней солями жесткости, а также ванализе опыта практической эксплуатации таких установок. Объекты:магнитная система тороидального типа, магнитное поле, ионы солей, содержащихся в воде, установки магнитной водоочистки. Методы:тороидальная электродинамика; эксперименты по взаимодействию тороидальных электромагнитных объектов;гипотезы об электрохимических процессах, происходящих в водном потоке, протекающем вдоль оси магнитного тороида;эксперименты по проверке этих гипотез;теория, объясняющая технологию магнитной водоочистки; анализ многолетней практики эксплуатации установок «Магнуст». Результаты.Дано теоретическое объяснение технологии магнитной водоподготовки с помощью тороидальных магнитных установок. Описаны электрохимические процессы, происходящие на этапе магнитной обработки и на последующем этапе нагревания омагниченной воды. Показано, что в присутствии магнитного поля ионы разных знаков дрейфуют во взаимно противоположных направлениях. По этой причине образование гидрокарбонатов кальция и магния на поверхности нагревателя затруднено.Как следствие, не происходит и отложения карбонатов на нагреваемых поверхностях.Определена наиболее эффективная конструкция магнитной установки, ее оптимальные параметры. Приведены сведения об эксплуатации установок «Магнуст» на нескольких бытовых и производственных объектах.

Long-Distance Ultrafast Spin Transfer over a Zigzag Carbon Chain Structure.

Using high-level abinitio quantum theory we suggest an optically induced subpicosecond spin-transfer scenario over 4.428nm, a distance which is directly comparable to the actual CMOS scale. The spin-density transfer takes place between two Ni atoms and over a 40-atom-long zigzag carbon chain. The suitable combination of the local symmetries of the participating carbon atoms and the global symmetry of the whole molecule gives rise to what we term the dynamical Goodenough-Kanamori rules, allowing the long-range coupling of the two Ni atoms. We also present local spin-flip scenarios, and compare spin flip and spin transfer with respect to their sensitivity against an external static magnetic gradient. Finally, we use two identical laser pulses, rather than a single one, which allows us to accurately control local (intrasite) vs global (intersite) processes, and we thus solve the problem of embedding individually addressable molecular nanologic elements in an integrated nanospintronic circuit. Our results underline the great potential of carbon chain systems as building and supporting blocks for designing future all-optical magnetic processing units.

Orientation Estimation by Partial-State Updating Kalman Filter and Vectorial Magnetic Interference Detection

Attitude estimation based on a magnetic and inertial measurement unit is popular in the areas of robotics, aerospace, and unmanned aerial vehicles. Nevertheless, the magnetometer is prone to external magnetic disturbance that deteriorates the state estimation. This article proposes a novel partial state update strategy in the extended Kalman filter (PS-EKF) by optimally solving the posteriori covariance optimization problem under the Kalman gain constraint, so as to obviate the magnetic measurement update on two level angles and the inertial sensor biases. Besides, a new magnetic disturbance detection technique (vectorial detector) considering both the norm and the direction of the magnetometer measurement is proposed. Simulations and experiments show that the proposed PS-EKF method can be totally immune to the magnetic interference on the level angles and sensors biases, in contrast to the traditional extended Kalman filter using either the direct magnetic output or the indirect yaw as the measurement.

3D printed magnetically-actuating micro-gripper operates in air and water

The emerging trend towards miniaturization of robotic grippers is motivated by the needs for precise manipulation of smaller objects within confined spaces. However, it faces a multitude of challenges in micro-fabricating, assembling, and actuating the grippers with increasingly smaller dimensions. To overcome these challenges, we report here a method to 3D print a magnetically-driven triple-finger micro-gripper for robust micro-manipulation in air and water. Magnetic actuation was chosen for its advantage of untethered operation in complex surroundings. Mitigating the trade-off between mechanical compliance and magnetic actuation forces, the monolithic micro-gripper design comprising compliant mechanical flexures and magnetic force actuation units was rapidly fabricated using micro-continuous liquid interface production (μCLIP) process. Finally, we attached the 3D printed gripper to a robotic arm and demonstrated its ability to manipulate micro objects both air and water. This work may enable potential biological and biomedical applications such as operation of live cells and soft tissues.

Discussion on Roundness of Non-Ferromagnetic Tube by Interior Magnetic Abrasive Finishing Using a Magnetic Machining Jig

In this study, mainly researching the improvement of roundness of thick SUS304 stainless steel tube by interior magnetic abrasive finishing using a magnetic machining jig. The influence of reciprocating velocity of magnetic pole unit on the improvement of roundness of interior surface was studied by establishing the dynamic equation of magnetic machining jig. Experimental results showed that low reciprocating velocity of magnetic pole unit is conducive to the improvement of interior roundness of the thick SUS304 stainless steel tube. The reason is that the low reciprocating velocity of magnetic pole unit reduces the pitch of the helical motion and can produce greater finishing force of the magnetic machining jig.

Simultaneous End User Calibration of Multiple Magnetic Inertial Measurement Units With Associated Uncertainty

A fast method to simultaneously calibrate multiple MEMS Magnetic Inertial Measurement Units (MIMUs) accurately in the field is needed in many application areas. The MEMS MIMUs require calibration of systematic errors of bias, sensitivity, non-orthogonality and misalignment, which vary with temperature and use. Even after calibration, the sensors undergo stochastic errors in static and dynamic conditions and thus uncertainty of output must also be modeled. We propose a method for easy and fast calibration of multiple MIMUs together, while mounted on a single platform. The precise alignment of sensors is not assumed. Our method calibrates both fixed array of MEMS MIMUs or many independent MIMUs simultaneously using kinematic constraints. The novelty of our approach is that the uncertainty of sensors output is also learned as part of our model. Compared with existing state-of-art methods, our algorithm gives more consistent readings of all MIMUs and our framework also predicts the associated uncertainty of the sensor output. The uncertainty prediction of individual sensors is particularly helpful in the sensor fusion.

A Full-State Robust Extended Kalman Filter for Orientation Tracking During Long-Duration Dynamic Tasks Using Magnetic and Inertial Measurement Units.

Accurate and robust orientation estimation using magnetic and inertial measurement units (MIMUs) has been a challenge for many years in long-duration measurements of joint angles and pedestrian dead-reckoning systems and has limited several real-world applications of MIMUs. Thus, this research aimed at developing a full-state Robust Extended Kalman Filter (REKF) for accurate and robust orientation tracking with MIMUs, particularly during long-duration dynamic tasks. First, we structured a novel EKF by including the orientation quaternion, non-gravitational acceleration, gyroscope bias, and magnetic disturbance in the state vector. Next, the a posteriori error covariance matrix equation was modified to build a REKF. We compared the accuracy and robustness of our proposed REKF with four filters from the literature using optimal filter gains. We measured the thigh, shank, and foot orientation of nine participants while performing short- and long-duration tasks using MIMUs and a camera motion-capture system. REKF outperformed the filters from literature significantly (p < 0.05) in terms of accuracy and robustness for long-duration tasks. For example, for foot MIMU, the median RMSE of (roll, pitch, yaw) were (6.5, 5.5, 7.8) and (22.8, 23.9, 25) deg for REKF and the best filter from the literature, respectively. For short-duration trials, REKF achieved significantly (p < 0.05) better or similar performance compared to the literature. We concluded that including non-gravitational acceleration, gyroscope bias, and magnetic disturbance in the state vector, as well as using a robust filter structure, is required for accurate and robust orientation tracking, at least in long-duration tasks.

Magnetometer Robust Deep Human Pose Regression With Uncertainty Prediction Using Sparse Body Worn Magnetic Inertial Measurement Units

We propose a deep learning based framework that learns data-driven temporal priors to perform 3D human pose estimation from six body worn Magnetic Inertial Measurement units sensors. Our work estimates 3D human pose with associated uncertainty from sparse body worn sensors. We derive and implement a 3D angle representation that eliminates yaw angle (or magnetometer dependence) and show that 3D human pose is still obtained from this reduced representation, but with enhanced uncertainty. We do not use kinematic acceleration as input and show that it improves the generalization to real sensor data from different subjects as well as accuracy. Our framework is based on Bi-directional recurrent autoencoder. A sliding window is used at inference time, instead of full sequence (offline mode). The major contribution of our research is that 3D human pose is predicted from sparse sensors with a well calibrated uncertainty which is correlated with ambiguity and actual errors. We have demonstrated our results on two real sensor datasets; DIP-IMU and Total capture and have come up with state-of-art accuracy. Our work confirms that the main limitation of sparse sensor based 3D human pose prediction is the lack of temporal priors. Therefore fine-tuning on a small synthetic training set of target domain, improves the accuracy.

Estimate Hand–Finger Position With One Magnetometer and Known Relative Orientation

Inertial-sensor-based hand motion tracking has become a well-accepted method in many clinical applications, including rehabilitation of the upper extremity. However, major drawbacks are that a sensor on each segment and kinematic chain rule is required. Thus, errors accumulate through the kinematic chain rule. Also, the length of each segment needs to be measured for each user. We propose a novel method in which a permanent magnet on the dorsal side of the hand combined with an inertial and magnetic measurement unit (IMMU) on the fingertip is used to estimate the position of the thumb and index fingertip relative to the position of the dorsal side of the hand. The biggest advantages of the proposed method are that no prior information and kinematic chain rule are needed. Besides, the required number of sensors is low. A Levenberg–Marquardt (L-M) approach is presented to estimate the relative positions with the known orientations. The performance is demonstrated in multiple experiments in which various movement tasks were performed. The most complex task in which participants performed reaching and grasping movements based on the action research arm test (ARAT) resulted in a median distance error between thumb and index finger of 9.6%.

A Simplified Extended Kalman Filter Used for Magnetic and Inertial Measurement Units

As a sensor unit, a magnetic and inertial measurement unit (MIMU) is mainly composed of a tri-axis gyroscope, a tri-axis accelerometer and a tri-axis magnetometer. The Extended Kalman Filter (EKF) is the currently preferred algorithm used to fuse the outputs of the MIMU sensor in order to determine the attitude of the MIMU's carrier platform. One of the main problems of the EKF is its high computational cost, which is largely due to solving the matrix inversion in the Kalman gain. This article simplifies the Kalman gain by ensuring it does not contain any matrices that would require an inversion operation. This is achieved by simplifying the linearized measurement matrix (the Jacobian matrix) through orthogonalizing the observation and reference vectors. The inversion of the matrix contained in the Kalman gain can then be mathematically derived and the derived matrix can eventually replace the matrix inversion, in order to avoid the inversion operation when the EKF is executed. The simplified EKF is compared to the traditional EKF experimentally and the results show that the simplified method has similar accuracy to the traditional method, but with a faster execution time.

Magnetic excitations affected by spin-lattice coupling in the S=32 triangular lattice antiferromagnet Ag2CrO2

${\mathrm{Ag}}_{2}{\mathrm{CrO}}_{2}$ is an $S=\frac{3}{2}$ triangular lattice antiferromagnet in which long-range magnetic order with a fivefold magnetic unit cell appears below the transition temperature (${T}_{\mathrm{N}}$) of 24 K. The long-range magnetic order is accompanied by a structural transition. Inelastic neutron scattering experiments were performed to investigate the magnetic interactions, anisotropy, and correlations in this material. Above ${T}_{\mathrm{N}}$, diffuse scattering originating from the short-ranged magnetic correlations consistent with a ${120}^{\ensuremath{\circ}}$ structure was observed. The magnetic excitations below ${T}_{\mathrm{N}}$ were reproduced reasonably well using a linear spin-wave model with further-neighbor interactions and easy-axis anisotropy, which are predicted to be due to a previously proposed spin-lattice coupling [Wang and Vishwanath, Phys. Rev. Lett. 100, 077201 (2008)].

Magnetic ordering of Ho and its role in the magnetization reversal and coercivity double peaks in the Ho3Fe5O12 garnet

Rare-earth based garnet system, Ho3Fe5O12 shows magnetization compensation phenomenon at Tcomp = 138 K and a magnetic transition at 50 K. In the present work, we reveal the physics of these low temperature magnetic transitions by carrying out detailed dc magnetization, ac susceptibility, neutron depolarization, and neutron diffraction studies. Interestingly, our dc magnetization study under low (≲ 50 Oe) magnetic fields has shown a previously unknown sign reversal of magnetization (below the Tcomp) that persists down to 5 K, the lowest measured temperature. Magnetic measurements under moderate fields between 50 Oe and 1 kOe reveal two compensation temperatures (in the range of 105 – 150 K depending upon the applied field value) leading to double magnetization reversals. Interestingly, for magnetic fields ≥ 1 kOe, these two compensation temperatures merge to a single Tcomp (=138 K). A modified Stoner-Wohlfarth model has been used to explain the asymmetrical nature of double peak around the Tcomp in the temperature dependent coercivity data. The ac susceptibility study supports the existence of both the transitions with an evidence of deep minimum at the Tcomp (138 K) and a broad peak at 50 K. Mesoscopic neutron depolarization study has revealed a zero domain-magnetization state at the Tcomp. Temperature dependent neutron diffraction study has revealed that Ho carries an induced moment above the Tcomp due to polarizing effect under the internal magnetic field of the two magnetically ordered Fe sublattices at 567 K, whereas a single umbrella type ordering of Ho sublattice moments appears below the Tcomp, resulting in the distortion of magnetic unit cell from cubic to rhombohedral symmetry. However, below 50 K, Ho3+ sites are divided into two inequivalent magnetic sublattices, having different moments and canting angles, and it leads to double umbrella type magnetic structure. Neutron diffraction study has revealed an asymmetric variation of the tetrahedral, octahedral, and dodecahedral sublattice moments resulting in a magnetization reversal at ~ 138 K which is very well supported by the mean field theory calculations. In the present study, we have resolved the ambiguity of magnetic ordering of the rare-earth (Ho3+) sublattice and its role in multiple magnetic transitions. The utility of such compensated ferrimagnetic materials in spin polarizers/analyzers and fast switching memory devices has been emphasized.

The Complex Structure of the Anterior White Commissure of the Human Brain: Fiber Dissection and Tractography Study

Commissural fibers are necessary for bilateral integration, body coordination, and complex cognitive information flow between the hemispheres. The anterior commissure (AC) has a complex architecture interconnecting areas of the frontal, temporal and occipital lobes. The present study aims to demonstrate the connections and the course of the anterior (ACa) and posterior (ACp) limb of the AC using fiber dissection and diffusion tensor imaging (DTI) of the human brain. Fiber dissection was performed in a stepwise manner from lateral to medial on 6 left hemispheres. The gray matter was decorticated and the ACa-ACp was exposed. The ACa and ACp tracts were demonstrated using a high-spatial-resolution DTI with a 3T magnetic resonance unit in 13 cases. Using both techniques showed that the AC has complex interconnections with large areas of the frontal (olfactory tubercles, anterior olfactory nucleus, olfactory bulb, and the orbital gyri), temporal (amygdaloidal nuclei, temporal and perirhinal cortex), and occipital (visual cortex) lobes. The ACp makes up the major component of the AC and is composed of temporal and occipital fibers. We observed that these fibers do not make a distinct bundle; the temporal fibers joined the uncinate fasciculus and the occipital fibers joined the sagittal striatum to reach their targets. Being aware of the course of the AC isimportant during transcallosal and interforniceal approaches to the third ventricle tumors and temporal lobe epilepsy surgery. The intermingling fibers of the AC can provide a better understanding of the unexplained deficit that may occur during regional surgery.

Structure and Magnetization Plateau of a Frustrated Co6 Cluster Antiferromagnet Sr2Co3(C2O4)3(OH)4·3H2O

A new frustrated spin-cluster antiferromagnet Sr2Co3(C2O4)3(OH)4·3H2O has been synthesized by the hydrothermal method. The basic magnetic unit of this compound is an isolated Co6 cluster, which is ...

Dispersion-Corrected DFT Methods for Applications in Nuclear Magnetic Resonance Crystallography.

Nuclear electric field gradient (EFG) tensor parameters depend strongly on electronic structures, making their calculation from first principles an excellent metric for the prediction, refinement, and optimization of crystal structures. Here, we use plane-wave density functional theory (DFT) calculations of EFG tensors in organic solids to optimize the Grimme (D2) and Tkatchenko-Scheffler (TS) atomic-pairwise force field dispersion corrections. Refinements using these new force field correction methods result in better representations of true crystal structures, as gauged by calculations of 177 14N, 17O, and 35Cl EFG tensors from 95 materials. The most striking result is the degree by which calculations of 35Cl EFG tensors of chloride ions match with experiment, due to the ability of these new methods to properly locate the positions of hydrogen atoms participating in H···Cl- hydrogen bonds. These refined structures also feature atomic coordinates that are more similar to those of neutron diffraction structures than those obtained from calculations that do not employ the optimized force fields. Additionally, we assess the quality of these new energy-minimization protocols for the prediction of 15N magnetic shielding tensors and unit cell volumes, which complement the larger analysis using EFG tensors, since these quantities have different physical origins. It is hoped that these results will be useful in future nuclear magnetic resonance (NMR) crystallographic studies and will be of great interest to a wide variety of researchers, in fields including NMR spectroscopy, computational chemistry, crystallography, pharmaceutical sciences, and crystal engineering.

Majorana modes in emergent-wire phases of helical and cycloidal magnet-superconductor hybrids

Noncollinear magnetism opens exciting possibilities to generate topological superconductivity. Here, we focus on helical and cycloidal magnetic textures in magnet-superconductor hybrid structures in a background magnetic field. We demonstrate that this system can enter a topological phase which can be understood as a set of parallel topological wires. We explore and confirm this idea in depth with three different approaches: a continuum model, a tight-binding model based on the magnetic unit cell, and exact diagonalization on a finite two-dimensional lattice. The key signature of this topological state is the presence of Majorana bound states at certain disclination defects in the magnetic texture. Based on the $C_2$ symmetry imposed by the helical or cycloidal texture, we employ the theory of topological crystalline superconductors with rotation invariants to obtain the Majorana parity at disclinations. Furthermore, we consider a 90-degree helimagnet domain wall, which is formed by a string of alternating disclinations. We discuss how the resulting chain of disclination bound states hybridizes into two chiral modes with different velocities. We suggest that hybrid systems of chiral magnets and superconductors are capable of hosting Majorana modes in various spatial configurations with potentially far less nano-engineering than in, e.g., semiconductor wires.