Magnetic Lattice Research Articles

R2Pt7MnP4-x (R = Ca, Eu): Intrinsic heterostructures based on a combination of AuCu3- and CaBe2Ge2-type fragments with chemically switchable magnetic interplay

Two quaternary phosphide platinides, Eu2Pt7MnP2.96 (I4/mmm, a = 4.0453(7) Å, c = 26.745(4) Å, V = 437.67(17) Å3, Z = 2, R1 = 0.0262, wR2 = 0.0527) and Ca2Pt7MnP3.02 (I4/mmm, a = 4.0027(5) Å, c = 26.735(5) Å, V = 428.34(14) Å3, Z = 2, R1 = 0.0280, wR2 = 0.0673) were synthesized as single crystals and bulk samples, their crystal structures were established from single-crystal X-ray diffraction data and confirmed by powder diffraction and elemental analysis. The compounds crystallize in the tetragonal system, and represent heterostructures built from the alternating layers of AuCu3- and CaBe2Ge2-type fragments. Both compounds are metallic based on the DFT calculations. Chemical bonding analysis reveals a pattern of covalent and ionic interactions within each compound. Magnetic measurements show both compounds to be ferromagnetic, and reveal an interplay between europium and manganese magnetic lattices, indicative of an exchange bias effect.

Stress Evaluation of Ferromagnetic Materials Based on a New Barkhausen Noise Sensor Composed by High Entropy Alloy Magnetic Core

Abstract During the service of ferromagnetic structural steel materials, stress should be evaluated accurately. Although the magnetic Barkhausen noise (MBN) testing has the ability to sense stress, it can be easily interfered with by environment. In this paper, a new MBN sensor is fabricated by selecting FeCoNi(AlMn)0.25 high entropy alloy (HEA) as the case of magnetic core to improve the accuracy of stress evaluation. The process optimization results show that the stability of MBN signal characteristics is the largest when the excitation frequency is 4 Hz and the voltage is 6 V. The signal-to-noise ratio of MBN indicates that the HEA and Ni-Zn ferrite probes have better anti-interference capability. The MBN signal characteristic values peak voltage and root mean square measured by the HEA probe can linearly quantify the stress level with higher efficiency, stability, and accuracy. The underlying reason of high sensitivity of HEA probe to the variation of MBN signals is revealed based on the magnetic properties. The microstructure and the thermodynamic parameters are analyzed to clarify whether the additions of Al and Mn atoms can affect the short-ranged magnetic exchange interaction and lattice distortion, which affects the magnetization behavior of HEA. Finally, the availability of MBN sensor with HEA magnetic core to the stress evaluation on the retired slide rails of car seats is conducted, which demonstrates its great application value.

Emergent elasticity and wavelike to particle-like crossover in a magnetic chiral soliton lattice

Emergent elasticity and wavelike to particle-like crossover in a magnetic chiral soliton lattice

Chemical Design of Spin Frustration to Realize Topological Spin Glasses.

Patterning spins to generate collective behavior is at the core of condensed matter physics. Physicists develop techniques, including the fabrication of magnetic nanostructures and precision layering of materials specifically to engender frustrated lattices. As chemists, we can access such exotic materials through targeted chemical synthesis and create new lattice types by chemical design. Here, we introduce a new approach to induce magnetic frustration on a modified honeycomb lattice through a competition of alternating antiferromagnetic (AFM) and ferromagnetic (FM) nearest-neighbor interactions. By subtly modulating these two types of interactions through facile synthetic modifications, we created two systems: (1) a topological spin glass and (2) a frustrated spin-canted magnet with low-temperature exchange bias. To design this unconventional magnetic lattice, we used a metal-organic framework (MOF) platform, Ni3(pymca)3X3 (NipymcaX where pymca = pyrimidine-2-carboxylato and X = Cl, Br). We isolated two MOFs, NipymcaCl and NipymcaBr, featuring canted Ni2+-based moments. Despite this similarity, differences in the single-ion anisotropies of the Ni2+ spins result in distinct magnetic properties for each material. NipymcaCl is a topological spin glass, while NipymcaBr is a rare frustrated magnet with low-temperature exchange bias. Density functional theory calculations and Monte Carlo simulations on the NipymcaX lattice support the presence of magnetic frustration as a result of alternating AFM and FM interactions. Our calculations enabled us to determine the ground-state spin configuration and the distribution of spin-spin correlations relative to paradigmatic kagomé and triangular lattices. This modified honeycomb lattice is similar to the electronic Kekulé-O phase in graphene and provides a highly tunable platform to realize unconventional spin physics.

Tilted-chiral-state-induced topological Hall effect in chiral magnetic soliton host Cr1/3TaS2

Chromium-intercalated Cr1/3TaS2 is well known for hosting a nontrivial chiral magnetic soliton lattice (CSL) with the reported highest Curie temperature (TC∼151 K) and strongest spin–orbit coupling, which has significant applications in gigahertz and high-speed spintronic devices. Herein, we thoroughly investigate the magneto-electrical transport properties of Cr1/3TaS2 single crystals. For H//ab, our magnetoresistance (MR) measurements reveal distinctive step-like behaviors, which are attributed to the formation and annihilation of chiral magnetic solitons. When under an oblique field, similar but weaker MR behaviors are observed compared to H//ab, indicating the appearance of an inclination-field-induced tilted-CSL. A topological Hall effect is observed under an oblique field, which is suggested to be induced by a nonzero topological charge density resulting from the tilted chiral states. The Cr1/3TaS2 offers an intriguing platform for studying the impact of chiral magnetic structures on magneto-electrical properties, which holds promise for both future spintronic device applications and fundamental investigation.

Magnetic Structure-Dependent Spin Texture Lattice in Hexagonal MnFeCoGe Magnets.

Topological spin textures are of great significance in magnetic information storage and spintronics due to their high storage density and low drive current. In this work, the transformation of magnetic configuration from chaotic labyrinth domains to uniform stripe domains was observed in MnFe1-xCoxGe magnets. This change occurs due to the noncollinear magnetic structure switching to a uniaxial ferromagnetic structure with increasing Co content, as identified by neutron diffraction results and Lorentz transmission electron microscopy (L-TEM). Of utmost importance, a hexagonal lattice of high-density robust type-II magnetic bubble lattice was established for x = 0.8 through out-of-plane magnetic field stimulation and field-cooling. The dimensions of the type-II magnetic bubbles were found to be tuned by the sample thickness. Therefore, the stabilization of complex magnetic spin textures, associated with enhanced uniaxial ferromagnetic interaction and magnetic dipole-dipole interaction in MnFe1-xCoxGe through magnetic structure manipulation, as further confirmed by the micromagnetic simulations, will provide a convenient and efficient strategy for designing topological spin textures with potential applications in spintronic devices.

Strain-induced antiferromagnetic domain switching via the spin Jahn-Teller effect

The spin Jahn-Teller effect, where a degeneracy of magnetic ground states is spontaneously lifted by structural distortions, lends itself to exploitation by the implied magnetoelastic coupling. CoTi2O5 hosts a frustrated topology of magnetic interactions that could realize such coupling, since the observed magnetic ground state requires a spontaneous monoclinic distortion of the crystal. Using resonant elastic x-ray scattering to simultaneously probe the magnetic structure and lattice distortion of CoTi2O5, we demonstrate near complete magnetic domain switching by an applied uniaxial stress that is conjugate to the monoclinic strain. Our results, supported by density functional theory calculations, confirm that CoTi2O5 displays spin Jahn-Teller effects that can be understood in terms of modulated Heisenberg exchange interactions, and demonstrate the potential functionality of spin Jahn-Teller materials in spintronic devices sensitive to uniaxial strain. Published by the American Physical Society 2024

Implementing nonlinear optics from Off-Energy closed orbit at NSLS-II

To characterize the second-order (chromatic sextupole) magnet lattice with high precision, we implemented nonlinear optics from off-energy closed orbit (NOECO) tool based on the linear optics from closed orbit modulation (LOCOM) method, named LOCOM-NOECO. The preliminary numerical study indicates that 1–2% precision can be achieved for the calibration of chromatic sextupoles. This accuracy could potentially help in resolving some long-standing challenges of NSLS-II (e.g., the discrepancy between the designed and measured dynamic apertures) if such high precision can be fulfilled. As an independent crosscheck, we also implemented NOECO based on the independent component analysis (ICA) method using turn-by-turn (TBT) BPM data, named ICA-NOECO. Both ICA-NOECO and LOCOM-NOECO have been successfully applied to identify the pre-dialed random errors of a chromatic sextupole family including five power supplies, and achieved the root mean square (RMS) residual error of 1% and peak error less than 2%. Moreover, to mitigate the chromatic sextupole error effect, we applied the correction and achieved significant improvements in the injection efficiency as well as the dynamic apertures.

Magnetic structure and lattice properties of R2Cu2In intermetallics (R = Dy, Tm, Lu)

Magnetic and structural properties of tetragonal R2Cu2In intermetallics are presented for R = Dy, Tm, and Lu. The neutron diffraction experiment clarifies the nature of magnetic order in Dy2Cu2In and Tm2Cu2In. While Tm2Cu2In orders ferromagnetically below TC = 31 K with magnetic space group (MSG) P4/mb'm', Dy2Cu2In forms a non-collinear ferromagnetic state below 50 K (MSG P2'/m') with another k = (½, ½, ½) component of magnetic moment (MSG Ibam.1'c) appearing at 20 K. The ground-state magnetic structure is described by the MSG Im'm'a with a magnetic moment of 9.35 μB. This subsequent transition is accompanied by the changes in the T-dependence of anisotropy constants, however, no related anomaly is observed in specific heat dominated by the CF and exchange interaction effects. Magnetic properties are discussed in the context of lattice response to temperature and pressure variations. The experimental results are supported by the analysis of the non-magnetic Lu analogue and by the first-principles calculations (electronic structure and material properties) based on Density Functional Theory (DFT).

Yu-Shiba-Rusinov bands in a self-assembled kagome lattice of magnetic molecules

Kagome lattices constitute versatile platforms for studying paradigmatic correlated phases. While molecular self-assembly of kagome structures on metallic substrates is promising, it is challenging to realize pristine kagome properties because of hybridization with the bulk degrees of freedom and modified electron-electron interactions. We suggest that a superconducting substrate offers an compelling platform for realizing a magnetic kagome lattice. Exchange coupling induces kagome-derived bands at the interface, which are protected from the bulk by the superconducting energy gap. We realize a magnetic kagome lattice on a superconductor by depositing Fe-porphin-chloride molecules on Pb(111) and using temperature-activated de-chlorination and self-assembly. This allows us to control the formation of smaller kagome precursors and long-range ordered kagome islands. Using scanning tunneling microscopy and spectroscopy at 1.6 K, we identify Yu-Shiba-Rusinov states inside the superconducting energy gap and track their hybridization from the precursors to larger islands, where the kagome lattice induces extended YSR bands. These YSR-derived kagome bands inside the superconducting energy gap allow for long-range coupling and induced pairing correlations, motivating further studies to resolve possible spin-liquid or Kondo-lattice-type behavior.

Detailed dynamics of a moving magnetic skyrmion lattice in MnSi observed using small-angle neutron scattering under an alternating electric current flow

Detailed dynamics of a moving magnetic skyrmion lattice in MnSi observed using small-angle neutron scattering under an alternating electric current flow

Electron holography observation of individual ferrimagnetic lattice planes.

Atomic-scale observations of a specific local area would be considerably beneficial when exploring new fundamental materials and devices. The development of hardware-type aberration correction1,2 in electron microscopy has enabled local structural observations with atomic resolution3-5 as well as chemical and vibration analysis6-8. In magnetic imaging, however, atomic-level spin configurations are analysed by electron energy-loss spectroscopy by placing samples in strong magnetic fields9-11, which destroy the nature of the magnetic ordering in the samples. Although magnetic-field-free observations can visualize the intrinsic magnetic fields of an antiferromagnet by unit-cell averaging12, directly observing the magnetic field of an individual atomic layer of a non-uniform structure is challenging. Here we report that the magnetic fields of an individual lattice plane inside materials with a non-uniform structure can be observed under magnetic-field-free conditions by electron holography with a hardware-type aberration corrector assisted by post-digital aberration correction. The magnetic phases of the net magnetic moments of (111) lattice planes formed by opposite spin orderings between Fe3+ and Mo5+ in a ferrimagnetic double-perovskite oxide (Ba2FeMoO6) were successfully observed. This result opens the door to direct observations of the magnetic lattice in local areas, such as interfaces and grain boundaries, in many materials and devices.

Effect of tetragonality on the magnetic preference, elasticity and magnetocrystalline anisotropy of L10-FeM(M = Ni, Pd, Pt) alloys

The effect of tetragonality on the magnetocrystalline anisotropy of L10-FeM(M = Ni, Pd and Pt) ordered alloys is widely concerned, but its effect on other physical properties is not well understood. In this paper, the impact of tetragonality on the magnetic preference, lattice dynamics and elasticity, as well as magnetocrystalline anisotropy of these L10 ordered alloys are systematically investigated based on the first-principles methods. The antiferromagnetic FeNi and FePd alloys are metastable within appropriate axial ratio c/a range, although the ferromagnetic state is ground-state stable. The reduced axial ratio c/a favors the antiferromagnetic state over the ferromagnetic state for the FePt alloy. The tetragonality has a non-monotonic effect on the Young’s modulus and shear modulus, while the bulk modulus is almost tetragonality independent for all L10 ordered alloys. The uniaxial magnetocrystalline anisotropy increases with tetragonality in the fe rromagnetic state, while it shows different trends in the antiferromagnetic state. Interestingly, the antiferromagnetic FePt exhibits planar magnetocrystalline anisotropy in a wide axial ratio c/a range, and a transition between hard magnetic and semi-hard magnetic at c/a = 1.45 is discovered for the FePd alloy. These intriguing properties induced by tetragonality provide us a deeper understanding of the potential rare-earth-free permanent magnet L10 alloys.

Transition Metal-Based Dimeric Metallosurfactants: From Organic-Inorganic Hybrid Structures and Low-Dimensional Magnets to Metallomicelles.

The dimeric (gemini) as well as metallosurfactants exhibit enhanced physicochemical properties compared with conventional surfactants. By uniting the benefits of both, a series of novel dimeric metallosurfactants of the type (12-2-12)[MBr4] (M = Co, Ni, Cu and Zn) was successfully prepared by the reaction of the dimeric surfactant bis(N,N-dimethyl-N-dodecyl)ethylene-1,2-diammonium dibromide, 12-2-12, and the MBr2 salt. Structures and magnetic properties of the materials were studied comprehensively in the solid state, while their micellization was explored in solution. The obtained results unveil that the incorporation and the choice of transition metal more significantly influence surfactants' structures ((12-2-12)2+ cations adopt V-, U-, or trans-conformations) and the magnetic features (metal ions form 1D or 2D magnetic lattice) than their solution properties. However, all synthesized metallosurfactants display improved self-assembly properties compared with the metal-free precursor. The investigated systems represent a fruitful platform for the development of multifunctional materials as they are simple to produce, can be obtained in high yields, and show advanced properties both in solution and in the solid state. Notably, this work unveils a simple approach to the design and synthesis of novel low-dimensional magnetic systems of great potential for future spintronic and optoelectronic devices.

Simulation-trained machine learning models for Lorentz transmission electron microscopy

Understanding the collective behavior of complex spin textures, such as lattices of magnetic skyrmions, is of fundamental importance for exploring and controlling the emergent ordering of these spin textures and inducing phase transitions. It is also critical to understand the skyrmion–skyrmion interactions for applications such as magnetic skyrmion-enabled reservoir or neuromorphic computing. Magnetic skyrmion lattices can be studied using in situ Lorentz transmission electron microscopy (LTEM), but quantitative and statistically robust analysis of the skyrmion lattices from LTEM images can be difficult. In this work, we show that a convolutional neural network, trained on simulated data, can be applied to perform segmentation of spin textures and to extract quantitative data, such as spin texture size and location, from experimental LTEM images, which cannot be obtained manually. This includes quantitative information about skyrmion size, position, and shape, which can, in turn, be used to calculate skyrmion–skyrmion interactions and lattice ordering. We apply this approach to segmenting images of Néel skyrmion lattices so that we can accurately identify skyrmion size and deformation in both dense and sparse lattices. The model is trained using a large set of micromagnetic simulations as well as simulated LTEM images. This entirely open-source training pipeline can be applied to a wide variety of magnetic features and materials, enabling large-scale statistical studies of spin textures using LTEM.

Theory of Collective Excitations in the Quadruple-Q Magnetic Hedgehog Lattices.

Hedgehog and antihedgehog spin textures in magnets behave as emergent monopoles and antimonopoles, which give rise to astonishing transport and electromagnetic phenomena. Using the Kondo-lattice model in three dimensions, we theoretically study collective spin-wave excitation modes of magnetic hedgehog lattices which have recently been discovered in itinerant magnets such as MnSi_{1-x}Ge_{x} and SrFeO_{3}. It is revealed that the spin-wave modes, which appear in the subterahertz regime, have dominant amplitudes localized at Dirac strings connecting hedgehog-antihedgehog pairs and are characterized by their translational oscillations. It is found that their spectral features sensitively depend on the number and configuration of the Dirac strings and, thus, can be exploited for identifying the topological phase transitions associated with the monopole-antimonopole pair annihilations.

Topological polarons in halide perovskites.

Halide perovskites emerged as a revolutionary family of high-quality semiconductors for solar energy harvesting and energy-efficient lighting. There is mounting evidence that the exceptional optoelectronic properties of these materials could stem from unconventional electron-phonon couplings, and it has been suggested that the formation of polarons and self-trapped excitons could be key to understanding such properties. By performing first-principles simulations across the length scales, here we show that halide perovskites harbor a uniquely rich variety of polaronic species, including small polarons, large polarons, and charge density waves, and we explain a variety of experimental observations. We find that these emergent quasiparticles support topologically nontrivial phonon fields with quantized topological charge, making them nonmagnetic analog of the helical Bloch points found in magnetic skyrmion lattices.

Synchrotron infrared nanospectroscopy in fourth-generation storage rings.

Fourth-generation synchrotron storage rings represent a significant milestone in synchrotron technology, offering outstandingly bright and tightly focused X-ray beams for a wide range of scientific applications. However, due to their inherently tight magnetic lattices, these storage rings have posed critical challenges for accessing lower-energy radiation, such as infrared (IR) and THz. Here the first-ever IR beamline to be installed and to operate at a fourth-generation synchrotron storage ring is introduced. This work encompasses several notable advancements, including a thorough examination of the new IR source at Sirius, a detailed description of the radiation extraction scheme, and the successful validation of our optical concept through both measurements and simulations. This optimal optical setup has enabled us to achieve an exceptionally wide frequency range for our nanospectroscopy experiments. Through the utilization of synchrotron IR nanospectroscopy on biological and hard matter samples, the practicality and effectiveness of this beamline has been successfully demonstrated. The advantages of fourth-generation synchrotron IR sources, which can now operate with unparalleled stability as a result of the stringent requirements for producing low-emittance X-rays, are emphasized.

Jahn-Teller magnets with charge transfer

We develop a unified approach to description of Jahn-Teller (JT) magnets – compounds based on JT d-ions with t 2g n1 e g n2 type configurations in a highly symmetrical octahedral, cubic, or tetrahedral environment and ground state orbital E-doublet. Rich variety of their phase states: non-magnetic and magnetic insulators, multiferroics, strange metals and unconventional superconductors is related to the instability of their highly symmetric JT “progenitors” to charge transfer with anti-JT d-d disproportionation and formation of a system of effective local composite spin-singlet or spin-triplet S-type bosons moving in a non-magnetic or magnetic lattice. We present a short overview of physical properties for actual JT-magnets.

Spectrum of Gyrotropic Modes and Energy Transfer between Dipolar‐Coupled Magnetic Vortices in a Square Lattice via Triggered Vortex Gyration: A Promise for Spintronics Technology

AbstractThe atoms in a crystal lattice vibrate together and generate vibrational modes known as acoustic and optical phonon modes. Similarly, collective vortex gyration motion can be generated in artificial magnetic vortex lattices, created from periodically arranged nanodisks of specific dimensions and aspect ratios. This study uses micromagnetic simulations to characterize the spectra of gyrotropic modes in two‐dimensional magnetic vortex‐based, tailor‐made square lattice arrangements. The shifting of mode frequencies and mode splitting is witnessed depending on the vortex configurations in the lattice. The obtained gyrotropic modes are analogous to two‐dimensional square lattice structures exhibiting acoustic and optical phonon modes. The dynamics of magnetic vortices are also discussed in the transfer of magnetic energy at three points along the three high symmetry directions of the lattice when the central magnetic vortex is excited by a spin‐polarized current with an excitation frequency equal to the collective gyrotropic frequencies of the vortices. Similar to the higher contribution of acoustic phonon modes in the heat transmission process in a crystal lattice, acoustic‐like gyrotropic modes transfer more energy than optical‐like gyration modes in the vortex lattices. These magnetic metastructures hold promise for novel applications in magnetic waveguides and information processing devices, as well as for advancing spintronics.