Magnetic Origin Research Articles

The lithium-rich giant stars puzzle: New observational trends for a general-mass-loss scenario

The existence of one percent of lithium-rich giant stars among normal, lithium-poor giant stars continues to be poorly explained. By merging two catalogues - one containing 10,535 lithium-rich giant stars with lithium abundances ranging from 1.5 to 4.9\,dex, and the other detecting infrared sources - we have found 421 clump giant stars and 196 first-ascending giant stars with infrared excesses indicating stellar mass losses. The clump stars are the most lithium-rich. Approximately 5.8 percent of these stars appear to episodically lose mass in periods of approximately $\,years or less, while the remaining stars ceased their mass loss and maintained their lithium for nearly $\,years. We propose a scenario in which all giant stars with masses below two solar masses undergo prompt lithium enrichment with mass-ejection episodes. We suggest that the mass loss results from internal angular-momentum transport. It is possible that a transitory instability, perhaps of magnetic origin, rapidly transports the nuclear material responsible for the lithium enrichment to the stellar surface and triggers shell ejections. Additionally, the strong mass loss in some lithium-rich stars during their evolution activates their chromospheres, as observed in ultraviolet spectra. Furthermore, intense episodical mass losses in these stages led to the observable formation of complex organic and inorganic particles, as detected in near-infrared spectra. In contrast to first-ascending giant stars, helium flashes during the clump can contribute to additional lithium enrichment alongside the aforementioned process. The combination of these two lithium sources may explain the much higher observed lithium abundances in clump stars, as well as their observed infrared excesses. If our scenario --based on a universal and rapid lithium enrichment episode process-- is correct, it could explain the rarity of lithium-rich giant stars.

Simultaneous Development of Antiferromagnetism and Local Symmetry Breaking in a Kagome Magnet (Co0.45Fe0.55)Sn.

CoSn and FeSn, two kagome-lattice metals, have recently attracted significant attention as hosts of electronic flat bands and emergent physical properties. However, current understandings of their physical properties are limited to knowledge of the average crystal structure. Here, we report the Fe-doping induced coemergence of the antiferromagentic (AFM) order and local symmetry breaking in (Co0.45Fe0.55)Sn. Rietveld analysis on the neutron and synchrotron X-ray diffraction data indicates A-type antiferromagnetic order with the moment pointing perpendicular to the kagome layers, associated with the anomaly in the MSn(1)2Sn(2)4 (M = Co/Fe) octahedral distortion and the lattice constant c. Reverse Monte Carlo (RMC) modeling of the synchrotron X-ray total scattering results captured the subtle local orthorhombic distortion involving off-axis displacements of Sn(2). Our results indicate that the stable hexagonal lattice above TN becomes unstable once the A-type AFM order is formed below TN. We argue that the local symmetry breaking has a magnetic origin, since the spatially varied M-Sn(2) bond lengths arise from out-of-plane magnetic exchange coupling Jc via the exchange pathway M-Sn(2)-M. Our study provides comprehensive information on the crystal structure in both long-range scale and local scale, unveiling unique coupling between AFM order, octahedral distortion, and hidden local symmetry breaking.

Effect of Fe doping on the electronic properties of CoSn Kagome semimetal.

Quantum phenomena in two-dimensional Kagome materials lead to exotic topological states and complex magnetism. Here, we have investigated the detailed electronic properties of Co$_{1-x}$Fe$_x$Sn with Fe doping to explore the competing electronic interactions for the origin of complex magnetism and topological properties. We find that the screening effect in the valence electrons increases while the correlation effect decreases with an increase in the doping concentration ($x$). Valence fluctuations observed at Co and Fe L$_{2,3}$ edges showed systematic changes in the magnitude of divalent and trivalent states with the increase in $x$. Fe $3d$ states are more screened by the conduction electrons than the Co $3d$ states. A comparison of the theoretical and experimental density of states showed different natures of localized states with dominating screening effects on the surface and dominating correlation effects in the bulk for $x$~$>$~0. We have observed localized flat bands on the CoSn (001) surface while quasi-localized flat bands on the Co$_{0.94}$Fe$_{0.06}$Sn (001) surface. The distinct character of the bulk and surface band structure is confirmed in the Fe-doped composition. Hence, the bulk-surface interaction present in Co$_{1-x}$Fe$_x$Sn gives rise to the origin of valence fluctuation, complex magnetism, and topological properties.

Magnetic property of tellurium-infiltrated Inconel 718: First-principles calculations and experimental validation

The fission product element tellurium in fourth-generation molten salt reactors is the primary cause of cracking in nickel-based high-temperature alloy components. This paper reports the emergence and origin of magnetism in the tellurium-infiltrated Inconel 718. The source of magnetism is identified through first-principles calculations. The accuracy of the theoretical calculations is confirmed by comparative magnetic attraction experiments. It indicates that the primary source of magnetism after tellurium infiltration is the generation of Cr3Te4 but not NiNbTe2. The magnetism generated by Cr3Te4 provides an additional driving force for their clustering distribution. This study facilitates the understanding of the mechanisms behind crack formation in nickel-based alloy components and potential solutions.

Kitaev interactions through extended superexchange pathways in the jeff=1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${j}_{{\\mathsf{eff}}}=1/2$$\\end{document} Ru3+ honeycomb magnet RuP3SiO11

Magnetic materials are composed of the simple building blocks of magnetic moments on a crystal lattice that interact via magnetic exchange. Yet from this simplicity emerges a remarkable diversity of magnetic states. Some reveal the deep quantum mechanical origins of magnetism, for example, quantum spin liquid (QSL) states in which magnetic moments remain disordered at low temperatures despite being strongly correlated through quantum entanglement. A promising theoretical model of a QSL is the Kitaev model, composed of unusual bond-dependent exchange interactions, but experimentally, this model is challenging to realise. Here we show that the material requirements for the Kitaev QSL survive an extended pseudo-edge-sharing superexchange pathway of Ru3+ octahedra within the honeycomb layers of the inorganic framework solid, RuP3SiO11. We confirm the requisite jeff=12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${j}_{{\\mathsf{eff}}}=\\frac{1}{2}$$\\end{document} state of Ru3+ in RuP3SiO11 and resolve the hierarchy of exchange interactions that provide experimental access to an unexplored region of the Kitaev model.

Theoretical Study of the Magnetic Mechanism of a Pca21 C4N3 Monolayer and the Regulation of Its Magnetism by Gas Adsorption.

For metal-free low-dimensional ferromagnetic materials, a hopeful candidate for next-generation spintronic devices, investigating their magnetic mechanisms and exploring effective ways to regulate their magnetic properties are crucial for advancing their applications. Our work systematically investigated the origin of magnetism of a graphitic carbon nitride (Pca21 C4N3) monolayer based on the analysis on the partial electronic density of states. The magnetic moment of the Pca21 C4N3 originates from the spin-split of the 2pz orbit from special carbon (C) atoms and 2p orbit from N atoms around the Fermi energy, which was caused by the lone pair electrons in nitrogen (N) atoms. Notably, the magnetic moment of the Pca21 C4N3 monolayer could be effectively adjusted by adsorbing nitric oxide (NO) or oxygen (O2) gas molecules. The single magnetic electron from the adsorbed NO pairs with the unpaired electron in the N atom from the substrate, forming a Nsub-Nad bond, which reduces the system's magnetic moment from 4.00 μB to 2.99 μB. Moreover, the NO adsorption decreases the both spin-down and spin-up bandgaps, causing an increase in photoelectrical response efficiency. As for the case of O2 physisorption, it greatly enhances the magnetic moment of the Pca21 C4N3 monolayer from 4.00 μB to 6.00 μB through ferromagnetic coupling. This method of gas adsorption for tuning magnetic moments is reversible, simple, and cost-effective. Our findings reveal the magnetic mechanism of Pca21 C4N3 and its tunable magnetic performance realized by chemisorbing or physisorbing magnetic gas molecules, providing crucial theoretical foundations for the development and utilization of low-dimensional magnetic materials.

First-principle study origin of ferromagnetism in non-magnetic perovskite BaSnO3 doped with 2p-X (X=C, N)

In this study, our goal is to analyze the origin of magnetization in non magnetic cubic structure perovskite BaSnO3 doped with 2p-X (X=C, N) using the full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). For the exchange and correlation potential we have applied the generalized gradient approximation (GGA) and the GGA plus-modified Becke-Johnson potential (mBJ-GGA). The results show that BaSnO3 doped with C then with N and finally with C and N exhibit half-metallic ferromagnetism behavior with the integer magnetic moment of 1, 2 and 3 μB per cell respectively. The origin of the ferromagnetism that occurs within these compounds is mainly caused by the p-p hybridization between 2p-impurities and its neighboring oxygen atoms. These results allowed to conclude that doped perovskite could provide a new type of materials, called half-metallic for future spintronic devices.

Spin Spiral State at a Ferromagnetic Gd Vacuum Interface.

Centrosymmetric bulk magnets made of layered Gd intermetallics had been discovered recently to exhibit helical spin spirals with a wavelength of ≈2 nm that transform into skyrmion lattices at certain magnetic fields. Here we report on the observation of a spin spiral state at the Gd(0001) surface. Spin-polarized scanning tunneling microscopy images show striped regions with a periodicity of about 2nm. These stripes rearrange upon application of an external magnetic field, thereby unambiguously confirming their magnetic origin. Density functional theory calculations explain that competing exchange interactions in the surface layer of Gd(0001) together with a magnetovolume fine-tuning of the exchange interaction to the next Gd layer favor a chiral 2nm conical spin spiral at the surface, arising as a general behavior of the Gd monolayer.

Origin of magnetism via cation vacancy defects in non-stoichiometric NiCo2O4 nanoparticles: A synchrotron-based x-ray absorption and x-ray magnetic circular dichroism spectroscopic study

The present study probes the effect of cation distributions in the structural, optical, electronic, and magnetic properties of mixed-valent inverse-spinel NiCo2O4 (NCO) nanoparticles (NPs). NCO NPs were prepared using the sol–gel combustion method and the grain size was obtained in the magnetic exchange length range assumed to be from single-ion anisotropy. The Raman and photoluminescence spectroscopies confirm the presence of an inverse-spinel structure with different oxidation states, and vibrating sample magnetometry clarifies the existence of ferromagnetism with the presence of magnetic anisotropy among the cations. These NPs annealed at a higher grain-growth temperature accumulate ferrimagnetic properties and produce magneto-crystalline anisotropy making NCO an assuring material for spintronic applications. A detailed x-ray absorption spectroscopy and x-ray magnetic circular dichroism studies reveal an indestructible correlation between the distribution of the present cations and the element-specific origin of ferrimagnetic behavior. Ni is found to be accountable for the magnetic moment and electronic conduction, whereas Co is associated mainly with the generation of the magnetic anisotropy even in the polycrystalline NP form. This describes the anti-ferromagnetic coupling between Co and Ni ions that is pivotal in demonstrating the exchange interaction between these cations. The above result signifies the site-dependent cation valence states for the magnetic properties, and the extent of growing conditions are related to such cation-site dysfunction. This depicts further tunability in NCO as a functional oxide material.

Mapping the Longitudinal Magnetic Field in the Atmosphere of an Active Region Plage from the Inversion of the Near-ultraviolet CLASP2.1 Spectropolarimetric Data

We apply the HanleRT Tenerife Inversion Code to the spectropolarimetric observations obtained by the Chromospheric Layer Spectropolarimeter. This suborbital space experiment measured the variation with wavelength of the four Stokes parameters in the near-ultraviolet spectral region of the Mg ii h and k lines over a solar disk area containing part of an active region plage and the edge of a sunspot penumbra. We infer the stratification of the temperature, the electron density, the line-of-sight velocity, the microturbulent velocity, and the longitudinal component of the magnetic field from the observed intensity and circular polarization profiles. The inferred model atmosphere shows larger temperature and electron density in the plage and the superpenumbra regions than in the quiet regions. The shape of the plage region in terms of its brightness is similar to the pattern of the inferred longitudinal component of the magnetic field in the chromosphere, as well as to that of the overlying moss observed by the Atmospheric Imaging Assembly in the 171 Å band, which suggests a similar magnetic origin for the heating in both the plage and the moss region. Moreover, this heating is particularly significant in the regions with larger inferred magnetic flux. In contrast, in the superpenumbra, the regions with larger electron density and temperature are usually found in between these regions with larger magnetic flux, suggesting that the details of the heating mechanism in the chromosphere of the superpenumbra may be different from those in the plage, but with the magnetic field still playing a key role.

Electronic and magnetic origins of unconventional charge density wave in kagome FeGe

Electronic and magnetic origins of unconventional charge density wave in kagome FeGe

Copper Intercalation Induces Amorphization of 2D Cu/WO3 for Room‐Temperature Ferromagnetism

AbstractFerromagnetism in the two‐dimensional limit has become an intriguing topic for exploring new physical phenomena and potential applications. To induce ferromagnetism in 2D materials, intercalation has been proposed to be an effective strategy, which could introduce lattice distortion and unpaired spin into the material to modulate the magnetocrystalline anisotropy and magnetic exchange interactions. To strengthen the understanding of the magnetic origin of 2D material, Cu was introduced into a 2D WO3 through chemical intercalation in this work (2D Cu/WO3). In contrast to the diamagnetic nature of Cu and WO3, room‐temperature ferromagnetism was characterized for 2D Cu/WO3. Experimental and theoretical results attribute the ferromagnetism to the bound magnetic polaron in 2D Cu/WO3, which is consist of unpaired spins from W5+/W4+ with localized carriers from oxygen vacancies. Overall, this work provides a novel approach to introduce ferromagnetism into diamagnetic WO3, which could be applied for a wider scope of 2D materials.

Copper Intercalation Induces Amorphization of 2D Cu/WO3 for Room-Temperature Ferromagnetism.

Ferromagnetism in the two-dimensional limit has become an intriguing topic for exploring new physical phenomena and potential applications. To induce ferromagnetism in 2D materials, intercalation has been proposed to be an effective strategy, which could introduce lattice distortion and unpaired spin into the material to modulate the magnetocrystalline anisotropy and magnetic exchange interactions. To strengthen the understanding of the magnetic origin of 2D material, Cu was introduced into a 2D WO3 through chemical intercalation in this work (2D Cu/WO3). In contrast to the diamagnetic nature of Cu and WO3, room-temperature ferromagnetism was characterized for 2D Cu/WO3. Experimental and theoretical results attribute the ferromagnetism to the bound magnetic polaron in 2D Cu/WO3, which is consist of unpaired spins from W5+/W4+ with localized carriers from oxygen vacancies. Overall, this work provides a novel approach to introduce ferromagnetism into diamagnetic WO3, which could be applied for a wider scope of 2D materials.

Origin of Magnetism in a Supposedly Nonmagnetic Osmium Oxide.

A supposedly nonmagnetic 5d^{1} double perovskite oxide is investigated by a combination of spectroscopic and theoretical methods, namely, resonant inelastic x-ray scattering, x-ray absorption spectroscopy, magnetic circular dichroism, and multiplet ligand-field calculations. We found that the large spin-orbit coupling admixes the 5d t_{2g} and e_{g} orbitals, covalency raises the 5d population well above the nominal value, and the local symmetry is lower than O_{h}. The obtained electronic interactions account for the finite magnetic moment of Os in this compound and, in general, of 5d^{1} ions. Our results provide direct evidence of elusive Jahn-Teller distortions, hinting at a strong electron-lattice coupling.

Comprehensive analysis of the eclipsing binaries V527 Dra and V2846 Cyg

ABSTRACT This is the first comprehensive study of the eclipsing binaries V527 Dra and V2846 Cyg, based on radial velocities and ground- and space-based light curves. We perform detailed modeling of these data to derive the absolute parameters and the orbital properties of the two systems. V527 Dra is found to be a semidetached, and V2846 Cyg a contact binary. Both show continual out-of-eclipse variations that can be explained by migrating dark spots of magnetic origin. We also perform the eclipse timing variation (ETV) analysis which reveals that V527 Dra has a tertiary companion whose mass (${\sim} 1 \,{\rm M}_{\odot }$) and orbital inclination (${\sim} 70^{\circ }$) are additionally constrained by radial velocities. The ETV diagram of V2846 Cyg displays a quadratic trend accompanied by a low-amplitude cyclic variation, likely due to a magnetic cycle, although further eclipse times are needed to provide a clearer explanation. Lastly, we demonstrate a correlation between the variations in spot parameters obtained via light curve modelling for individual orbital cycles and the residual ETVs, essentially confirming the assumption of magnetic activity in both systems.

Realization of 2D multiferroic with strong magnetoelectric coupling by intercalation: a first-principles high-throughput prediction

The discovery of novel two-dimensional (2D) multiferroic materials is attractive due to their potential for the realization of information storage and logic devices. Although many approaches have been explored to simultaneously introduce ferromagnetic (FM) and ferroelectric (FE) orders into a 2D material, the resulting systems are often plagued by weak magnetoelectric (ME) coupling or limited room-temperature stability. Here, we present a superlattice strategy to construct non-centrosymmetric AM2X4 multiferroic monolayers, i.e., intercalating transition metal ions (A) into the tetragonal-like vacancies of transition metal dichalcogenide bilayers (MX2). Starting from 960 intercalated AM2X4 compounds, our high-throughput calculations have identified 21 multiferroics with robust magnetic order, large FE polarization, low transition barrier, high FE/FM transition temperature, and strong ME coupling. According to the origin of magnetism, we have classified them into twelve type-a, seven type-b, and two type-c multiferroics, which exhibit different ME coupling behavior. During the switching of polarization, the reversal of skyrmions chirality, the transition of the magnetic ground state from FM to antiferromagnetic, and the changes in spin-polarized electron distribution were observed in type-a, type-b, and type-c 2D multiferroic materials, respectively. These results substantially expand the family of 2D ferroic materials and pave an avenue for designing and implementing nonvolatile logic and memory devices.

An emission-state-switching radio transient with a 54-minute period

Long-period radio transients are an emerging class of extreme astrophysical events of which only three are known. These objects emit highly polarized, coherent pulses of typically a few tens of seconds duration, and minutes to approximately hour-long periods. Although magnetic white dwarfs and magnetars, either isolated or in binary systems, have been invoked to explain these objects, a consensus has not emerged. Here we report on the discovery of ASKAP J193505.1+214841.0 (henceforth ASKAP J1935+2148) with a period of 53.8 minutes showing 3 distinct emission states—a bright pulse state with highly linearly polarized pulses with widths of 10–50 seconds; a weak pulse state that is about 26 times fainter than the bright state with highly circularly polarized pulses of widths of approximately 370 milliseconds; and a quiescent or quenched state with no pulses. The first two states have been observed to progressively evolve over the course of 8 months with the quenched state interspersed between them suggesting physical changes in the region producing the emission. A constraint on the radius of the source for the observed period rules out an isolated magnetic white-dwarf origin. Unlike other long-period sources, ASKAP 1935+2148 shows marked variations in emission modes reminiscent of neutron stars. However, its radio properties challenge our current understanding of neutron-star emission and evolution.

Electronic Structure Using Powder XRD and Its Correlation with the Origin of Room-Temperature Magnetism in Cr3+ Doped SnO2

Electronic Structure Using Powder XRD and Its Correlation with the Origin of Room-Temperature Magnetism in Cr3+ Doped SnO2

Small-scale magnetic flux emergence preceding a chain of energetic solar atmospheric events

Context.Advancements in instrumentation have revealed a multitude of small-scale extreme-ultraviolet (EUV) events in the solar atmosphere and considerable effort is currently undergoing to unravel them.Aims.Our aim is to employ high-resolution and high-sensitivity magnetograms to gain a detailed understanding of the magnetic origin of such phenomena.Methods.We used coordinated observations from the Swedish 1-m Solar Telescope (SST), the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamics Observatory (SDO) to analyze an ephemeral magnetic flux emergence episode and the following chain of small-scale energetic events. These unique observations clearly link these phenomena together.Results.The high-resolution (0.″057 pixel−1) magnetograms obtained with SST/CRISP allowed us to reliably measure the magnetic field at the photosphere and to detect the emerging bipole that caused the subsequent eruptive atmospheric events. Notably, this small-scale emergence episode remains indiscernible in the lower resolution SDO/HMI magnetograms (0.″5 pixel−1). We report the appearance of a dark bubble in Ca IIK 3933 Å related to the emerging bipole, a sign of the canonical expanding magnetic dome predicted in flux emergence simulations. Evidence of reconnection are also found, first through an Ellerman bomb and later by the launch of a surge next to a UV burst. The UV burst exhibits a weak EUV counterpart in the coronal SDO/AIA channels. By calculating the differential emission measure (DEM), its plasma is shown to reach a temperature beyond 1 MK and to have densities between the upper chromosphere and transition region.Conclusions.Our study showcases the importance of high-resolution magnetograms in revealing the mechanisms that trigger phenomena such as EBs, UV bursts, and surges. This could hold implications for small-scale events similar to those recently reported in the EUV using Solar Orbiter. The finding of temperatures beyond 1 MK in the UV burst plasma strongly suggests that we are examining analogous features. Therefore, we recommend caution when drawing conclusions from full-disk magnetograms that lack the necessary resolution to reveal their true magnetic origin.

Temperature Dependence of Relativistic Valence Band Splitting Induced by an Altermagnetic Phase Transition.

Altermagnetic (AM) materials exhibit non-relativistic, momentum-dependent spin-split states, ushering in new opportunities for spin electronic devices. While the characteristics of spin-splitting are documented within the framework of the non-relativistic spin group symmetry, there is limited exploration of the inclusion of relativistic symmetry and its impact on the emergence of a novel spin-splitting in the band structure. This study delves into the intricate relativistic electronic structure of an AM material, α-MnTe. Employing temperature-dependent angle-resolved photoelectron spectroscopy across the AM phase transition, the emergence of a relativistic valence band splitting concurrent with the establishment of magnetic order is elucidated. This discovery is validated through disordered local moment calculations, modeling the influence of magnetic order on the electronic structure and confirming the magnetic origin of the observed splitting. The temperature-dependent splitting is ascribed to the advent of relativistic spin-splitting resulting from the strengthening of AM order in α-MnTe as the temperature decreases. This sheds light on a previously unexplored facet of this intriguing material.