Magnetic Spin Configurations Research Articles

Orbital-selective effect of spin reorientation on the Dirac fermions in a non-charge-ordered kagome ferromagnet Fe3Ge

Kagome magnets provide a fascinating platform for the realization of correlated topological quantum phases under various magnetic ground states. However, the effect of the magnetic spin configurations on the characteristic electronic structure of the kagome-lattice layer remains elusive. Here, utilizing angle-resolved photoemission spectroscopy and density functional theory calculations, we report the spectroscopic evidence for the spin-reorientation effect of a kagome ferromagnet Fe3Ge, which is composed solely of kagome planes. As the Fe moments cant from the c-axis into the ab plane upon cooling, the two kinds of kagome-derived Dirac fermions respond quite differently. The one with less-dispersive bands (kz ~ 0) containing the 3dz2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3{d}_{{z}^{2}}$$\\end{document} orbitals evolves from gapped into nearly gapless, while the other with linear dispersions (kz ~ π) embracing the 3dxz/3dyz components remains intact, suggesting that the effect of spin reorientation on the Dirac fermions has an orbital selectivity. Moreover, we demonstrate that there is no signature of charge order formation in Fe3Ge, contrasting with its sibling compound FeGe, a newly established charge-density-wave kagome magnet.

Atomic‐Scale Order and Disorder Induced Diverse Topological Spin Textures in Self‐Intercalated Van der Waals Magnets Cr1+δTe2

AbstractThe intercalation of magnetic atoms into van der Waals (vdW) gaps offers a versatile approach for manipulating local magnetic ordering in vdW magnets. However, these intercalated magnetic atoms are often intricately positioned within the gaps, resulting in an ambiguous impact on local magnetic interactions and spin configurations. Herein, the atomic and magnetic structures of self‐intercalated prototype materials Cr1+δTe2 are comprehensively investigated using transmission electron microscopy, elucidating the correlation between the concentration and distribution of intercalated Cr atoms and the evolution of spin textures. The observed transitions from topological Néel‐type skyrmions to non‐topological type‐II bubbles, and ultimately to trivial ferromagnetic domains, underscore the complex nature of these magnetic spin textures. The complexity of the local structural arrangements is further revealed through integrating atomic‐resolution imaging, revealing the disorder‐order‐disorder transitions manifested by the distribution of intercalated atoms. The modulation of intercalated atomic structure shapes the observed spin textures by affecting the Dzyaloshinskii−Moriya interaction (DMI), inter/intra‐layer coupling, and magnetic anisotropy. These findings provide profound insights into the structure‐magnetism relationship, offering promising avenues for engineering the magnetic properties of vdW magnets at the atomic level.

3DQuantum Anomalous Hall Effect in Magnetic Topological Insulator Trilayers of Hundred-Nanometer Thickness.

Magnetic topological states refer to a class of exotic phases in magnetic materials with the non-trivial topological property determined by magnetic spin configurations. An example of such states is the quantum anomalous Hall (QAH) state, which is a zero magnetic field manifestation of the quantum Hall effect. Current research in this direction focuses on QAH insulators with a thickness of less than 10nm. Here, molecular beam epitaxy (MBE) is employed to synthesize magnetic TI trilayers with a thickness of up to ≈106nm. It is found that these samples exhibit well-quantized Hall resistance and vanishing longitudinal resistance at zero magnetic field. By varying the magnetic dopants, gate voltages, temperature, and external magnetic fields, the properties of these thick QAH insulators are examined and the robustness of the 3D QAH effect is demonstrated. The realization of the well-quantized 3D QAH effect indicates that the nonchiral side surface states of the thick magnetic TI trilayers are gapped and thus do not affect the QAH quantization. The 3D QAH insulators of hundred-nanometer thickness provide a promising platform for the exploration of fundamental physics, including axion physics and image magnetic monopole, and the advancement of electronic and spintronic devices to circumvent Moore's law.

Magnetic structures and correlated physical properties in antiperovskites

Compounds with perovskite structures have become one of the focuses in both materials science and condensed matter physics because of their fascinating physical properties and potential functionalities correlated to magnetic structures. However, the understanding of the intriguing physical properties is still at an exploratory stage. Herein, owing to the magnetic frustration prompted by Mn6N or Mn6C octahedra, the abounding magnetic structures of antiperovskites, including collinear antiferromagnetic, collinear ferromagnetic, collinear ferrimagnetic, non-collinear magnetic, and non-coplanar magnetic spin configurations, are systematically introduced through the updated coverage. In addition, owing to the “spin-lattice-charge” coupling of antiperovskites, a large number of physical properties, such as anomalous thermal expansion, giant magnetoresistance, anomalous Hall effect, piezomagnetic/baromagnetic effects, magnetocaloric effect, barocaloric effect, etc ., are summarized by combining the discussions of the determined magnetic structures. This review aims to clarify the current research progress in this field, focusing on the relationship between the magnetic structures and the correlated physical properties, and provides the conclusion and outlook on further performance optimization and mechanism exploration in antiperovskites.

Understanding unconventional magnetic order in a candidate axion insulator by resonant elastic x-ray scattering

Magnetic topological insulators and semimetals are a class of crystalline solids whose properties are strongly influenced by the coupling between non-trivial electronic topology and magnetic spin configurations. Such materials can host exotic electromagnetic responses. Among these are topological insulators with certain types of antiferromagnetic order which are predicted to realize axion electrodynamics. Here we investigate the highly unusual helimagnetic phases recently reported in EuIn2As2, which has been identified as a candidate for an axion insulator. Using resonant elastic x-ray scattering we show that the two types of magnetic order observed in EuIn2As2 are spatially uniform phases with commensurate chiral magnetic structures, ruling out a possible phase-separation scenario, and we propose that entropy associated with low energy spin fluctuations plays a significant role in driving the phase transition between them. Our results establish that the magnetic order in EuIn2As2 satisfies the symmetry requirements for an axion insulator.

Signature of weakly coupled f electrons and conduction electrons in magnetic Weyl semimetal candidates PrAlSi and SmAlSi

Magnetic topological materials are a class of compounds with the underlying interplay of nontrivial band topology and magnetic spin configuration. Extensive interests have been aroused due to their application potential involved with an array of exotic quantum states. With angle-resolved photoemission spectroscopy and first-principles calculations, here we study the electronic properties of two magnetic Weyl semimetal candidates PrAlSi and SmAlSi. Though the two compounds harbor distinct magnetic ground states (ferromagnetic and antiferromagnetic for PrAlSi and SmAlSi, respectively) and 4$f$ shell fillings, we find that they share quite analogous low-energy band structure. By the measurements across the magnetic transitions, we further reveal that there is no evident evolution of the band structure in both compounds and the experimental spectra can be well reproduced by the nonmagnetic calculations, together suggesting a negligible effect of the magnetism on their electronic structures and a possibly weak coupling between the localized 4$f$ electrons and the itinerant conduction electrons. Our results offer essential insights into the interactions between magnetism, electron correlations, and topological orders in the $R$Al$X$ ($R$ = light rare earth and $X$ = Si or Ge) family.

Local cation order and ferrimagnetism in compositionally complex spinel ferrites

We present an exploration of a family of compositionally complex cubic spinel ferrites featuring combinations of Mg, Fe, Co, Ni, Cu, Mn, and Zn cations, systematically investigating the average and local atomic structures, chemical short-range order, magnetic spin configurations, and magnetic properties. All compositions result in ferrimagnetic average structures with extremely similar local bonding environments; however, the samples display varying degrees of cation inversion and, therefore, differing apparent bulk magnetization. Additionally, first-order reversal curve analysis of the magnetic reversal behavior indicates varying degrees of magnetic ordering and interactions, including potentially local frustration. Finally, reverse Monte Carlo modeling of the spin orientation demonstrates a relationship between the degree of cation inversion and the spin collinearity. Collectively, these observations correlate with differences in synthesis procedures. This work provides a framework for understanding magnetic behavior reported for “high-entropy spinels,” revealing many are likely compositionally complex oxides with differing degrees of chemical short-range order—not meeting the community established criteria for high or medium entropy compounds. Moreover, this work highlights the importance of reporting complete sample processing histories and investigating local to long-range atomic arrangements when evaluating potential entropic mixing effects and assumed property correlations in high entropy materials.

Regulating the Spin State of FeIII Enhances the Magnetic Effect of the Molecular Catalysis Mechanism.

Aqueous-phase oxygen evolution reaction (OER) is the bottleneck of water splitting. The formation of the O-O bond involves the generation of paramagnetic oxygen molecules from the diamagnetic hydroxides. The spin configurations might play an important role in aqueous-phase molecular electrocatalysis. However, spintronic electrocatalysis is almost an uncultivated land for the exploration of the oxygen molecular catalysis process. Herein, we present a novel magnetic FeIII site spin-splitting strategy, wherein the electronic structure and spin states of the FeIII sites are effectively induced and optimized by the Jahn-Teller effect of Cu2+. The theoretical calculations and operando attenuated total reflectance-infrared Fourier transform infrared (ATR FT-IR) reveal the facilitation for the O-O bond formation, which accelerates the production of O2 from OH- and improves the OER activity. The Cu1-Ni6Fe2-LDH catalyst exhibits a low overpotential of 210 mV at 10 mA cm-2 and a low Tafel slope (33.7 mV dec-1), better than those of the initial Cu0-Ni6Fe2-LDHs (278 mV, 101.6 mV dec-1). With the Cu2+ regulation, we have realized the transformation of NiFe-LDHs from ferrimagnets to ferromagnets and showcase that the OER performance of Cu-NiFe-LDHs significantly increases compared with that of NiFe-LDHs under the effect of a magnetic field for the first time. The magnetic-field-assisted Cu1-Ni6Fe2-LDHs provide an ultralow overpotential of 180 mV at 10 mA cm-2, which is currently one of the best OER performances. The combination of the magnetic field and spin configuration provides new principles for the development of high-performance catalysts and understandings of the catalytic mechanism from the spintronic level.

Dependence of band gaps in d -electron perovskite oxides on magnetism

Understanding the controlling principles of band gaps trends in d electron perovskites is needed both for gauging metal-insulator transitions, as well as their application in catalysis and doping. The magnitude of this band gap is rather different for different magnetic spin configurations. We find via electronic structure theory that the factors that connect gapping magnitudes to magnetism depend on the nature of the band edge orbital character (BEOC) and surprisingly scale with the number of antiferromagnetic contacts z$_i$ between neighboring transition metal ions. The dependence is weak when the BEOC are (d,d)-like ("Mott insulators"), whereas this dependence is rather strong in (p,d)-like ("charge transfer" insulators). These unexpected rules are traced to the reduced orbital interactions through the increase in the number of antiferromagnetic contacts between transition metal ions. The impact of magnetic order is not limited to the band gap magnitude and includes also the magnitude of lattice distortions connected to the electronic structure. These results highlight the importance of establishing in electronic structure theory of gap-related phenomena (doping, transport, metal-insulator transitions, conductive interfaces) the appropriate magnetic order.

Progress and prospects in magnetic topological materials.

Magnetic topological materials represent a class of compounds with properties that are strongly influenced by the topology of their electronic wavefunctions coupled with the magnetic spin configuration. Such materials can support chiral electronic channels of perfect conduction, and can be used for an array of applications, from information storage and control to dissipationless spin and charge transport. Here we review the theoretical and experimental progress achieved in the field of magnetic topological materials, beginning with the theoretical prediction of the quantum anomalous Hall effect without Landau levels, and leading to the recent discoveries of magnetic Weyl semimetals and antiferromagnetic topological insulators. We outline recent theoretical progress that has resulted in the tabulation of, for the first time, all magnetic symmetry group representations and topology. We describe several experiments realizing Chern insulators, Weyl and Dirac magnetic semimetals, and an array of axionic and higher-order topological phases of matter, and we survey future perspectives.

Epitaxial ferroelectric interfacial devices

Ferroelectric interfacial devices consist of materials systems whose interfacial electronic properties (such as a 2D electron gas or an interfacial magnetic spin configuration) are modulated by a ferroelectric layer set in its immediate vicinity. While the prototypical example of such a system is the ferroelectric field effect transistor first proposed in the 1950s, only with the recent advances in the controlled growth of epitaxial thin films and heterostructures, and the recent physical understanding down to the atomic scale of screening processes at ferroelectric-semiconducting and -metallic interfaces made possible by first principles calculations, have the conditions been met for a full development of the field. In this review, we discuss the recent advances in ferroelectric interfacial systems with emphasis on the ferroelectric control of the electronic properties of interfacial devices with well ordered (epitaxial) interfaces. In particular, we consider the cases of ferroelectric interfacial systems aimed at controlling the correlated state, including superconductivity, Mott metallic-insulator transition, magnetism, charge, and orbital order, and charge and spin transport across ferroelectric tunnel junctions. The focus is on the basic physical mechanisms underlying the emergence of interfacial effects, the nature of the ferroelectric control of the electronic state, and the role of extreme electric field gradients at the interface in giving rise to new physical phenomena. Such understanding is key to the development of ferroelectric interfacial systems with characteristics suitable for next generation electronic devices based on controlling the correlated state of matter.

New nanosized (Gd3+, Sm3+) co-doped zinc ferrite: Structural, magnetic and first-principles study

ZnFe2-x-yGdxSmyO4 (x = y = 0.01) ferrite nanoparticles with average size of 5 nm are synthesized by the co-precipitation method for the first time. X-Ray Diffractometer (XRD) revealed the formation of single-phase spinel with a high crystallinity. Fourier Transform Infrared (FTIR) confirmed the formation of spinel matrix crystallographic sites and Transmission Electron Microscopy (TEM) confirmed the formation of agglomerated spherical particles with nanometric sizes. The analysis of magnetic properties indicates a week ferrimagnetic behavior at low temperatures, while a superparamagnetic behavior is observed at high temperatures. The blocking temperature value is 55 K. A DFT study was performed on the normal, mixed and Sm–Gd co-doped spinel zinc ferrite using the GGA + U method to evaluate their ground state magnetic spin configuration and the effect of Sm3+ and Gd3+ doping on the structural, magnetic and electronic properties of zinc ferrite nanoparticles. It is found that the nanomaterial is most likely to adopt a ferrimagnetic spin arrangement with a degree of inversion close to 0.5. These results suggest that this material has significant function in the industry, which could be beneficial in point of view for telecommunication applications.

Interplay between defect transport and cation spin frustration in corundum-structured oxides

Despite the fundamental importance of mass transport, there is still a lack of knowledge regarding the mechanisms in many materials. In particular, how the magnetic spin structure interacts with migrating defects is unclear. Here, using density functional theory to examine cation interstitial transport in antiferromagnetic corundum-structured oxides, we reveal an interplay between the migration of the interstitial and the magnetic structure of the oxide. The magnetic spin configuration impacts the migration energy of the migrating defect but, critically, the defect modifies the spin configuration. Thus, the two aspects change in concert to modify one another. This has profound implications for mass transport in magnetic materials.

Skyrmion bubble states and their magnetic spin configuration manipulation in the C-interstitial MnNiGa alloy

Magnetic skyrmion bubbles are swirling magnetic textures with novel characteristics suitable for future applications in spintronic devices. Here, high-density nanometric bubbles are obtained by adding C element in biskyrmion-host MnNiGa materials. Furthermore, the diversified topological spin configurations of nanometric bubbles are manipulated by combining electric current with perpendicular magnetic fields. Different magnetic bubble states including the homogeneous skyrmion bubble state are achieved via electromagnetic manipulation. Via analysing the different magnetic textures obtained via electromagnetic manipulation, we infer that the topological spin configurations of magnetic bubbles are closely related to the relative intensity of external fields applied as magnetic bubbles nucleate.

Magnetic properties of layered chiral topological magnetic material Cr<sub>1/3</sub>NbS<sub>2</sub>

With the discovery and development of topological materials, topological physics has attracted enormous research interest in the fields of contemporary condensed matter physics. Topological property, which describes such a property that physical quantity remains invariant under continuous transformation (such as Chern number), has been revealed in a variety of materials, including topological insulators, topological semimetals (such as Weyl or Dirac semimetals), topological magnetic materials, etc. One-dimensional chiral magnetic soliton, similar to magnetic skyrmion, is a type of magnetic configuration with topological origin and quasi-particle property, which has shown tremendous physical properties and device functionalities. In this review, we mainly focus on a chiral helimagnet, called Cr<sub>1/3</sub>NbS<sub>2</sub>, which possesses chiral magnetic soliton lattice and other more spin configurations under different conditions. We systematically summarize the work on Cr<sub>1/3</sub>NbS<sub>2</sub>, discussing its crystal symmetry, band structure, magnetic interactions, rich magnetic phases, and the physics of associated phase transitions. In particular, the layered crystal structure of Cr<sub>1/3</sub>NbS<sub>2</sub> enables us to control the soliton number through tuning the layer number or crystal thickness. Our review provides a comprehensive summary of Cr<sub>1/3</sub>NbS<sub>2</sub> in order to draw more attention to this interesting material. Moreover, we envision that our work could offer useful guidance to the researchers working on topological and chiral magnetic materials, and thus introducing topological or chiral magnetism into two-dimensional layered materials and promoting the development of modern magnetism and spintronics. Therefore, this review mainly focuses on a magnet, called Cr<sub>1/3</sub>NbS<sub>2</sub>. We systematically summarize the work on Cr<sub>1/3</sub>NbS<sub>2</sub>, discussing its crystal symmetry, band structure, magnetic interaction, rich magnetic phases and the interesting physical phenomena occurring at each phase transition. In addition, the layered crystal structure of Cr<sub>1/3</sub>NbS<sub>2</sub> also enables us to use the layer number or crystal thickness to modulate and control its rich magnetic phases. We believe that our review provides a comprehensive summary of Cr<sub>1/3</sub>NbS<sub>2</sub>, which can make people have a better understanding of a typical topological magnetic material, thereby enriching the material types of magnets and low-dimensional material family and promoting the development of magnetism and spintronics applications, such as in magnetic memory devices, spintronic devices, and quantum information devices.

Possible magneto-mechanical and magneto-thermal mechanisms of ion channel activation in magnetogenetics.

The palette of tools for perturbation of neural activity is continually expanding. On the forefront of this expansion is magnetogenetics, where ion channels are genetically engineered to be closely coupled to the iron-storage protein ferritin. Initial reports on magnetogenetics have sparked a vigorous debate on the plausibility of physical mechanisms of ion channel activation by means of external magnetic fields. The criticism leveled against magnetogenetics as being physically implausible is based on the specific assumptions about the magnetic spin configurations of iron in ferritin. I consider here a wider range of possible spin configurations of iron in ferritin and the consequences these might have in magnetogenetics. I propose several new magneto-mechanical and magneto-thermal mechanisms of ion channel activation that may clarify some of the mysteries that presently challenge our understanding of the reported biological experiments. Finally, I present some additional puzzles that will require further theoretical and experimental investigation.

Effect of Write Head Movement On Magnetic Spin Domain Reversal of Nanocube Co/Pd Alloy Material Using Micromagnetic Simulation

An analysis of the effect of the write head movement on the reversal time of the domain spin with magnetic Co/Pd on the magnetic recording layer has been carried out through micromagnetic simulation. The magnetic recording layer is modeled in the form of cubes (nanocubes) which consists of 5 domain spin. The write head, which is a transduser, moves along the domain spin to write data in the form of magnetic spins, which represent the bits on the magnetic recorder perpendicular. The results of this simulation are a profile of changes in the total magnetic field and reversal time of the domain spin when writing magnetic data for 6 nanoseconds. The calculation used in this study is an analytical calculation regarding the reversal time of the magnetic domain spin of the Co/Pd alloy material. The formulation for calculating the reversal time of domain-spin magnetization is a combination of graphical analysis and analytical calculations with visualization of the magnetic spin configuration that consisting of 5 domains spin. This simulation was carried out using the finite element method and obtained a saturation 5 field value of the magnetic alloy Co/Pd (Hs) material of 2.5 x 105 A/m and a write head (Hwh) field that 6 must be applied to the magnetic recording layer in order to reverse the uniform domain spin is 7.3 x 106 A/m. Each size of the domain spin requires a different write head, the smaller the nanocube size, the greater the write head field applied to the magnetic recording layer. Meanwhile, the effective write head 6 field amplitude that is suitable for the 20 nm domain spin is 8.3 x 106 A/m. A significant change in the total field occurs when the domain spin reverses 3 times in the first domain spin (n1), the third domain spin (n3) and the fifth domain spin (n5). The total field value when t=0.42 ns ( first domain spin reversal) is 73.69376 A/m, then the total field at t=0.42 ns (third domain spin reversal) is 3443.197 A/m and the current total field t=0.42 ns (fifth domain spin reversal) of 5480.696 A/m.

Magnetic and magnetocaloric properties of Gd1-xYx2NiSi3 compounds (x = 0.25, 0.5, 0.75)

Abstract In this work, we report the magnetic dilution effect on the magnetic and magnetocaloric properties of Gd 1 - x Y x 2 NiSi 3 (x = 0.25, 0.5, 0.75) compounds by partial substitution of Y ions in Gd 2 NiSi 3 . The X-ray diffraction studies indicate all theses compounds form in AlB 2 type hexagonal crystal structure. The dc magnetic measurements reveal the compounds undergo antiferromagnetic like phase transition below 11.5, 7.2, and 3.1 K for x = 0.25, 0.5 and 0.75 compositions, respectively. The magnetic ground state of the compounds becoming increasingly fragile with the increase in Y concentration, and results in magnetic field induced ferromagnetic transition. Such change in magnetic spin configuration is responsible for moderately large magnetic entropy change ( Δ S M ∼ 19.3 J/kg-K, 14.8 J/kg-K and 9.8 J/kg-K for x = 0.25, 0.5, and 0.75, respectively, for Δ H = 7 T) in the cryogenic temperature region. The relative cooling power (RCP) has also been estimated for all the compounds that appears to be modest ( ∼ 503 J/kg for 7 T magnetic field change) for x = 0.25 analogue and reduces further with magnetic dilution effect caused by Y substitution.

Crystal Structure Prediction of Magnetic Transition-Metal Oxides by Using Evolutionary Algorithm and Hybrid DFT Methods.

Although numerous crystal structures have been successfully predicted by using currently available computational techniques, prediction of strongly correlated systems such as transition-metal oxides remains a challenge. To overcome this problem, we have interfaced evolutionary algorithm-based USPEX method with the CRYSTAL code, enabling the use of Gaussian-type localized atomic basis sets and hybrid density functional (DFT) methods for the prediction of crystal structures. We report successful crystal structure predictions of several transition-metal oxides (NiO, CoO, α-Fe2O3, V2O3, and CuO) with correct atomic magnetic moments, spin configurations, and structures by using the USPEX method in combination with the CRYSTAL code and Perdew–Burke–Ernzerhof (PBE0) hybrid functional. Our benchmarking results demonstrate that USPEX + hybrid DFT is a suitable combination to reliably predict the magnetic structures of strongly correlated materials.

High microwave absorption characteristic nanomaterial preparation and mechanism analysis

Due to the excellent microwave absorption characteristics, YIG has a broad prospect in microwave application. This paper successfully synthesized YIG nanoparticles with the average size of 68.2 nm. The size uniformity of nanoparticles was verified and calculated by TEM and XRD. Microwave absorption value reached up to -34.5 dB, which was far more than microwave absorption threshold value (−10 dB). The mechanism of high microwave absorption characteristics discovered in the study is derived from four aspects: (a) Multiple scattering and interfacial polarization of YIG nanoparticles on surfaces. (b) High coercivity and high magnetic loss parameters of YIG nanoparticles in the high frequency region. (c) Magnetic loss mechanism and ferromagnetic resonance of YIG. (d) The influence of lesser pinning site caused by smaller grain size. The study found that the fundamental reasons of FMR spectrum asymmetric behavior come from three factors: (І) Nanoparticles random orientation. (П) Different easy axis. (Ш) Non-uniform resonance modes in the process of YIG synthesis. It was observed that microwave absorption markedly reduced due to the influence of skin effect and temperature. The effects of temperature on skin depth and microwave absorption are because of different amounts of excited electrons from the valence band and different magnetic spin configurations. The mechanism of the effect of temperature on the resistance of YIG was discovered, which is derived from electron hoping mechanism, remnant phases influence, the effect of the lattice atoms thermal vibration and skin effect.