Magnetic Evolution Research Articles

Braking index of PSR J1846−0258: a model of magnetic inclination evolution and its gravitational-wave implication

We explain the braking index n=2.19±0.03 of PSR J1846−0258 by incorporating the time evolution of its magnetic inclination angle and dipolar magnetic field. Based on observational timing data and the age of the associated supernova remnant (tSNR≈1.77kyr), we estimate a magnetic inclination change rate of χ̇≈0.281°/100yrs, comparable to that of the Crab pulsar. Applying the two-dipole model to PSR J1846−0258, we find an internal dipole moment ratio η=M2/M1∼1026–1027. For magnetic field decay timescales τD<3.6×105 yrs, the magnetic energy dissipation rate (Ėmag∼(1033–1034) erg/s) partially explains the observed X-ray luminosity LX∼1.9×1034 erg/s, while longer τD requires additional energy sources. The derived gravitational wave strain (h0∼10−29) remains undetectable with current instruments but constrains internal magnetic field geometries. This work highlights the critical role of magnetic inclination dynamics in pulsar spin-down behavior and offers a physically motivated framework that can be extended to other young neutron stars with measured magnetic inclination and braking indices.

Multifunctional Hollow Carbon Microspheres Enable Superior Electromagnetic Wave Response and Corrosion Barrier.

Electromagnetic (EM) wave absorbing materials with corrosion barrier exhibit immense potential in meeting the requirements of electronic defense technology in the complex marine environments, but still confront conflicts in disentangling the trade-off of multifunctional applications. Herein, hollow carbon microspheres (HCMs) that simultaneously possess superior EM wave absorption and anti-corrosion capability have been produced with the aid of self-sacrificing templates. During the pyrolysis, the reductive characteristic of Zn microspheres and thermal driving force promote magnetic domain evolution, which enables optimized hetero-interface resonance and strong magnetic interactions, facilitating a minimum reflection loss lower than -40 dB and a wide absorption bandwidth greater than 5 GHz. Furthermore, HCMs-900 with both anion-repulsion characteristics and better resistance can partially reduce the adsorption/accumulation of corrosive species and decrease the charge-carrying ability, and the inevitably generated by-products of layered double hydroxides with strong anion-capture ability can hinder the access of corrosive species to the substrate surface, resulting in superior anti-corrosion capability. This innovative strategy inspires us with a motivated pathway for the rational design of advanced multifunctional anti-corrosive EM absorbing materials.

Sensitive strain effect on magnetic phase transitions in Sb-doped MnBi4Te7 magnetic topological insulator

Recent experiments have successfully fabricated ferromagnetic topological insulator MnBi4Te7 by Sb doping. However, distinct conclusions regarding magnetic phase transitions at different doping concentrations have emerged, alongside controversial interpretations of ferromagnetic origin. Based on first-principles calculations, we demonstrate that the evolution of magnetism in Sb-doped MnBi4Te7 is not only attributed to Mn–Bi/Sb antisite defects, as observed in some experiments, but is also significantly influenced by strain effects. Furthermore, our results reveal that magnetic phase transition is accompanied by a change from n-type to p-type charge carriers at Sb doping concentrations exceeding 30%, in excellent agreement with experimental observation. Moreover, Sb substitution leads to an obvious difference in the effective mass of charge carriers, which qualitatively coincides with experimentally measured carrier mobility. Additionally, Sb doping results in more delocalized charge carriers due to the relatively weaker Sb–Te bonding. Based on these findings, we further discuss how the enhanced carrier delocalization influences interlayer magnetic coupling, leading to a nonmonotonic evolution of long-range magnetism from antiferromagnetic to ferromagnetic and back to antiferromagnetic phases with increased Sb concentration.

Doping Effects on Magnetic and Electronic Transport Properties in (Ba1-xRbx)(Zn1-yMny)2As2 (0.1 ≤ x, y ≤ 0.25).

Diluted magnetic semiconductors (DMSs) represent a significant area of interest for research and applications in spintronics. Recently, DMSs derived from BaZn2As2 have garnered significant interest due to the record Curie temperature (TC) of 260 K. However, the influence of doping on their magnetic evolution and transport characteristics has not been thoroughly investigated. This study aims to fill this gap through susceptibility and magnetization measurements, electric transport analysis, and muon spin relaxation and rotation (µSR) measurements on (Ba1-xRbx)(Zn1-yMny)2As2 (0.1 ≤ x, y ≤ 0.25, BRZMA). Key findings include the following: (1) BRZMA showed a maximum TC of 138 K, much lower than (Ba,K)(Zn,Mn)2As, because of a reduced carrier concentration. (2) A substantial electromagnetic coupling is evidenced by a negative magnetoresistance of up to 34% observed in optimally doped BRZMA. (3) A 100% static magnetic ordered volume fraction is achieved in the low-temperature region, indicating a homogeneous magnet. (4) Furthermore, a systematic and innovative methodology has been initially proposed, characterized by clear step-by-step instructions aimed at enhancing TC, grounded in robust experimental findings. The findings presented provide valuable insights into the spin-charge interplay concerning magnetic and electronic transport properties. Furthermore, they offer clear direction for the investigation of higher TC DMSs.

Doping Effects on Magnetic and Electronic Transport Properties in BaZn2As2

Novel diluted magnetic semiconductors derived from BaZn2As2 are of considerable importance owing to their elevated Curie temperature of 260 K, the diversity of magnetic states they exhibit, and their prospective applications in multilayer heterojunctions. However, the transition from the intrinsic semiconductor BaZn2As2 (BZA) to its doped compounds has not been extensively explored, especially in relation to the significant intermediate compound Ba(Zn,Mn)2As2 (BZMA). This study aims to address this gap by performing susceptibility and magnetization measurements, in addition to electronic transport analyses, on these compounds in their single crystal form. Key findings include the following: (1) carriers can significantly modulate the magnetism, transitioning from a non-magnetic BZA to a weak magnetic BZMA, and subsequently to a hard ferromagnet (Ba,K)(Zn,Mn)2As2 with potassium (K) doping to BZMA; (2) two distinct sets of metal-insulator transitions were identified, which can be elucidated by the involvement of carriers and the emergence of various magnetic states, respectively; and (3) BZMA exhibits colossal negative magnetoresistance, and by lanthanum (La) doping, a potential n-type (Ba,La)(Zn,Mn)2As2 single crystal was synthesized, demonstrating promising prospects for p-n junction applications. This study enhances our understanding of the magnetic interactions and evolutions among these compounds, particularly in the low-doping regime, thereby providing a comprehensive physical framework that complements previous findings related to the high-doping region.

Tunable Bifurcation of Magnetic Anisotropy and Bi-Oriented Antiferromagnetic Order in Kagome Metal GdTi_{3}Bi_{4}.

The novel kagome family RTi_{3}Bi_{4} (R: rare-earth metals) offers a unique platform for exploring distinctive physical phenomena such as anisotropy, spin density wave, and anomalous Hall effect. In particular, the magnetic frustration and behavior of magnetic anisotropy in antiferromagnetic (AFM) kagome materials are of great interest for the fundamental studies and hold promise for next-generation device applications. Here, we report a tunable bifurcation of magnetic anisotropic and bi-oriented AFM order observed in the quasi-1D kagome antiferromagnet GdTi_{3}Bi_{4}. The magnetic domain evolutions during two plateau transition processes are directly visualized, unveiling a pronounced in-plane anisotropy along the a axis. Temperature-dependent characterization reveals a bifurcation transition of anisotropy at approximately 2K, where the a-axis anisotropy splits into two special orientations, revealing a hidden bi-oriented in-plane AFM order that deviates from the high-symmetry direction by ±7°. More intriguingly, the characteristics of the bifurcated anisotropy are clearly illustrated through vector magnetic field modulation, revealing three distinct in-plane domain phases in the transverse magnetic field phase diagram. Our results not only provide valuable insights into the tunable bifurcation of magnetic anisotropic in GdTi_{3}Bi_{4}, but also pave a novel pathway for AFM spintronics development.

Magnetic braking and dynamo evolution of β Hydri

The evolution of magnetic braking and dynamo processes in subgiant stars is essential for understanding how these stars lose angular momentum. In this work, we investigate the magnetic braking and dynamo evolution of the G-type subgiant β Hyi to test the hypothesis of weakened magnetic braking and the potential rejuvenation of large-scale magnetic fields. We analyzed spectropolarimetric observations from the polarimetric mode of High Accuracy Radial velocity Planet Searcher (HARPSpol) and combined them with archival X-ray data and asteroseismic properties from Transiting Exoplanet Survey Satellite (TESS) to estimate the current wind-braking torque of β Hyi. Despite experiencing weakened magnetic braking during the second half of its main-sequence lifetime, our results indicate that β Hyi has regained significant magnetic activity and a large-scale magnetic field. This observation aligns with the “born-again” dynamo hypothesis. Furthermore, our estimated wind braking torque is considerably stronger than what would be expected for a star in the weakened magnetic braking regime. This suggests that subgiants with extended convective zones can temporarily re-establish large-scale dynamo action. These results provide critical constraints on stellar rotation models and improve our understanding of the interplay between magnetic field structure, stellar activity cycles, and angular momentum evolution in old solar-type stars.

Structural and magnetic evolution in Ga+3-doped DyMnO3: Impact on Jahn-Teller distortion and spin glass behaviour

Structural and magnetic evolution in Ga+3-doped DyMnO3: Impact on Jahn-Teller distortion and spin glass behaviour

Evolution of phonon, magnetism, and electronic excitations across the insulator-to-metal transition in Ru(Br 1−x I x ) 3

Evolution of phonon, magnetism, and electronic excitations across the insulator-to-metal transition in Ru(Br <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:math> I <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mi>x</mml:mi></mml:msub></mml:math> ) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi/><mml:mn>3</mml:mn></mml:msub></mml:math>

Nonvolatile Electric Control of Ferromagnetism in Van Der Waals Multiferroic Heterostructures at Room Temperature.

Multiferroic heterostructures offer a promising platform for next-generation low-power spintronic devices by enabling electric-field control of magnetism. While recent advances in two-dimensional (2D) van der Waals (vdW) magnetic and ferroelectric materials have sparked significant interest, achieving reliable and nonvolatile electrical modulation of magnetism at room temperature within vdW multiferroic heterostructures remains a substantial challenge. Here, this study demonstrates robust, reproducible, and nonvolatile electrical control of ferromagnetism in Fe3GaTe2/CuInP2S6 multiferroic heterostructures under ambient conditions. The modulation is evidenced macroscopically by reshaped magnetic hysteresis loops in anomalous Hall voltage measurements and microscopically by in situ magnetic and electric field-induced domain evolution captured via magnetic force microscopy. The first-principles calculations reveal that the polarization of CuInP2S6 induces a significant modulation of the Dzyaloshinskii-Moriya interaction (DMI) in Fe3GaTe2. Incorporating these effects into micromagnetic simulations reproduces key features of the experimental hysteresis behaviors, indicating that the polarization-enhanced DMI lowers domain wall formation energy and drives a transition from coherent to incoherent magnetic reversal. These findings not only surmount the challenge of electrically modulating ferromagnetism in vdW systems via remanent ferroelectric polarization at room temperature but also open new pathways for energy-efficient skyrmion manipulation and vdW spintronic device engineering.

Correlation Between Structure, Microstructure, and Magnetic Properties of AlCoCrFeNi High-Entropy Alloy

This study explores the crystal structure, microstructure and magnetic phase evolution of the AlCoCrFeNi high-entropy alloy (HEA), highlighting its potential for applications requiring tailored magnetic properties across diverse temperatures. Electron microscopy and X-ray diffraction revealed that the as-cast alloy’s microstructure comprises equiaxed grains with branching dendrites, showing compositional variations between interdendritic regions enriched in Al and Ni. Temperature-induced phase transformations were observed above room temperature, transitioning from body centered cubic (BCC) phases (A2 and B2) to a predominant FCC phase at higher temperatures, followed by recrystallization of the A2 phase upon cooling. Magnetization measurements showed a drop near 380 K, suggesting the Curie temperature of BCC phases, a peak at 830 K attributed to optimal magnetic alignment in the FCC phase, and a sharp decline at 950 K marking the transition to a paramagnetic state. Magnetic moment calculations provided insights into magnetic alignment dynamics, while low-temperature analysis highlighted the alloy’s magnetically soft nature, dominated by ferromagnetic contributions from the A2 phase. These findings underscore the strong interdependence of microstructural features and magnetic behavior, offering a foundation for optimizing HEAs for temperature-sensitive scientific and industrial applications.

Estimation of magnetization directions using a sequential approach with inversion of normalized source strength and Bayesian Monte Carlo method

Total magnetization direction is not only an important parameter in magnetic data analysis but also provides valuable insights into the magnetic mineral composition, structure, and evolution of its sources. However, this direction is often unknown in the presence of strong remanent magnetization. We develop a sequential approach comprising three steps to estimate the magnetization directions of sources. The spatial locations and shapes of the anomalous bodies are first determined using [Formula: see text]-norm inversion of normalized source strength (NSS). For each anomalous body, the three components of the magnetic anomalous vector are then obtained through a fast-forward calculation based on Poisson’s relation. Finally, a Bayesian Monte Carlo inversion of total-field data is used to estimate the unknown magnetization directions of all anomalous bodies and their associated uncertainties. A synthetic model consisting of two causative bodies with distinct total magnetization directions is tested to validate this approach. Moreover, we analyze the sensitivities of three magnetization parameters and comprehensively investigate the influences of several factors on the estimation results. A field data example using the total-field magnetic anomaly over the Black Hill Intrusive Complex is also studied. The results and analyses suggest that our approach is applicable to sources containing multiple bodies with varying magnetization directions. In addition, supplementary prior information is advisable for cases where the inversion of NSS is not suitable in the first step, such as when the source body is located at great depth or has an asymmetric shape.

Multi-temperature cooling performance of GdFeCo thin films with high magnetic entropy change and evolution of perpendicular magnetic anisotropy with thickness

Abstract To investigate the effect of thin film thickness on magnetic, magnetocaloric, and perpendicular magnetic anisotropy, we prepared Ta (5nm)/GdFeCo/Ta(5nm) heterostructure with GdFeCo thickness varying from 50 nm to 180 nm. The compensation temperature (Tcomp) and Curie temperature (Tc) shift significantly as the thickness increases. The temperature-dependent magnetization reveals that the Tcomp (224.74 K) is lower than room temperature for the 50 nm thin film, suggesting a CoFe-rich phase. The isothermal magnetic entropy change (|Sm|) is measured at both Tcomp and Tc corresponds to second order magnetic phase transition. |Sm| is found to be 0.24 J/kgK for 90 nm rises to 0.6 J/kgK for 180 nm. Doubling of the thickness from 90 nm to 180 nm results to increase in |Sm| of about 150%. In addition, a significant magnetic entropy change (0.31 J/kgK for 50 nm thin film @ 15 kOe field) is noticed near the Curie temperature for all thin films. For all higher thicknesses, a discernible change in magnetic entropy is observed at Tc. The magnetic anisotropy estimated using Hall effect and MOKE measurements demonstrates perpendicular magnetic anisotropy begins to dominate around room temperature for films with thickness greater than 90 nm as their compensation temperature falls around room temperature. We demonstrate GdFeCo thin films could potentially be suitable for multi-temperature magnetic cooling applications. &amp;#xD;&amp;#xD;

Merging plasmoids and nanojet-like ejections in a coronal current sheet

Forced magnetic reconnection is triggered by external perturbations, which are ubiquitous in the solar corona. This process plays a crucial role in the energy release during solar transient events, which are often associated with electric current sheets (CSs). The CSs can often disintegrate through the development of the tearing instability, which may lead to the formation of plasmoids (magnetic islands, or twisted flux ropes in 3D) in the nonlinear phase of evolution. However, the complexity of the dynamics and the magnetic and thermodynamic evolution due to the coalescence of the plasmoids are not fully understood. We explore the departure of the CS from its equilibrium configuration through a reconnection process characterized by the formation of plasmoids with a guide field, their mutual approach and eventual coalescence, and we investigate the complex magnetic topology and thermodynamic evolution in and around the merged plasmoids. We used a resistive magnetohydrodynamic simulation of a 2.5D current layer embedded in a stratified medium in the solar corona, incorporating field-aligned thermal conduction using the open-source code MPI-AMRVAC. Multiple levels of adaptive mesh-refined grids were used to resolve the fine structures that result during the evolution of the system. The instability in the CS was triggered by imposing impulsive velocity perturbations concentrated at three different locations in the upper half along the CS plane. This led to the formation of plasmoids and their later coalescence. We demonstrate that a transition from purely 2D reconnection to 2D reconnection with a guide field takes place at the interface between the plasmoids as the latter evolve from the pre-merger to the merged state. The small-scale, short-lived, and collimated outflows during the merging process share various physical properties with the recently discovered nanojets. The subsequent thermodynamic change within and outside the merged plasmoid region is governed by the combined effect of Ohmic heating, thermal conduction, and expansion/contraction of the plasma. Our results imply that impulsive perturbations in coronal CSs can be the triggering agents for the coalescence of plasmoids. This then leads to the subsequent magnetic and thermodynamic change in and around the CS.

Starspot Area Coverage: Correlation with Age and Spectral Type in FGK and M Stars

Abstract Starspots, analogous to sunspots, are surface manifestations of stellar magnetic activity. Their study provides crucial insights into stellar dynamo processes and the evolution of magnetic phenomena. However, due to limited data on magnetic activity across stellar lifetimes, the relationship between starspot area coverage and stellar properties remains underexplored. This work investigates the correlation between starspot area coverage and stellar age, effective temperature, and rotation period in FGK and M stars using data from Kepler and CoRoT. We utilized the starspot transit mapping method to analyze 11 stars, calculating starspot area coverage by integrating spot areas on the stellar surface. The average starspot coverage ranged from 4% to 29%, consistent with theoretical models of stellar magnetic evolution. Our analysis revealed a strong anticorrelation with stellar age (Spearman ρ = −0.80), confirming a significant decline in magnetic activity over time, but a weak anticorrelation between starspot coverage and rotation period. Regarding the relationship between absolute starspot area coverage and effective temperature, we found a moderate positive correlation (Spearman ρ = 0.40), with the majority of stars with an absolute area coverage of (2–4 ± 0.6) × 1010 km2. Incorporating starspot coverage into isochrone models could significantly improve stellar age estimates, especially for young stars. Moreover, these measurements are crucial for refining stellar dynamo models and advancing our understanding of magnetic field generation.

Birth-Related Subdural Hemorrhage in Asymptomatic Newborns: Magnetic Resonance Imaging Prevalence and Evolution of Intracranial and Intraspinal Localization.

Background: Neonatal birth-related intracranial subdural hemorrhages (SDHs) represent a form of bleeding inside the skull that occurs in newborns. This condition includes the extravasation of blood both in the encephalic parenchyma and in the extra-axial spaces. Recent studies have shown that SDH and particularly post-traumatic birth-related hemorrhages represent a frequent occurrence, but they are often asymptomatic. The gold standard for the diagnosis and follow-up of patients with SDH is multiparametric Magnetic Resonance Imaging. The aim of this study is to describe our experience by reporting several cases of SDH with different distribution and Central Nervous System involvement by the MRI of this pathology in infants up to 30 days of age. Methods: We analyzed the age and sex of the patients included in this study, the localization of SDH in different CNS areas, and their frequency using distribution plots and pie charts. Results: About the analysis of the SDH locations in the 32 patients, the most common location was the cerebellum (31/32, 96.9%), followed by parietal and occipital lobes (19/32, 59.4%; 18/32, 56.2%, respectively), falx cerebri (11/32, 34.4%), tentorium cerebelli (10/32, 31.2%), temporal lobes (6/32, 18.7%), and finally cervical and dorsal spine in the same patients (4/32, 12.5%). According to SDH locations, the patients were divided into supratentorial, infratentorial, both, and Spinal Canal. Conclusions: Our study confirmed the literature data regarding the neonatal birth-related SDH high frequency, but also allowed us to focus our attention on the rarest spinal SDH localizations with the same benign evolution.

Investigation of Magnetic Domain evolutions and Microstructural Changes in Pr-Dy-Cu Modified Nd-Fe-B Magnets

Abstract The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr58Dy 10Cu32 alloy was investigated through scanning electron microscope（ SEM） and in-situ magneto-optic Kerr effect (MOKE) microscopy. The modification treatment resulted in the formation of a smooth and continuous weakly magnetic grain boundary layer and the (Nd,Pr,Dy)2Fe14B main phase with a high magnetocrystalline anisotropy field, leading to an increased coercivity of 23 kOe. MOKE observations revealed that the dynamic evolution of the maze domain area under an external magnetic field varied significantly between the original and modified magnets. Compared with the original magnets, the modified magnets exhibited a slower decrease in maze domain area during magnetization and a slower increase during reverse magnetization, contributing to the observed coercivity enhancement.

High-resolution Observations of a Small-scale Cancellation Nanoflare: Supporting Evidence for the Cancellation Nanoflare Model

Abstract An analytical cancellation nanoflare model has recently been established to show the fundamental role that ubiquitous small-scale cancellation nanoflares play in solar atmospheric heating. Although this model is well supported by simulations, observational evidence is needed to deepen our understanding of cancellation nanoflares. We present observations of a small-scale cancellation nanoflare event, analyzing its magnetic topology evolution, triggers, and physical parameters. Using coordinated observations from the Solar Dynamics Observatory and Goode Solar Telescope, we identify a photospheric flow-driven cancellation event with a flux cancellation rate of ∼1015 Mx s−1 and a heating rate of 8.7 × 106 erg cm−2 s−1. The event shows the characteristic transition from π-shaped to X-shaped magnetic configuration before the formation of a 2″ current sheet, closely matching model predictions. This event provides critical observational support for the cancellation nanoflare model and its role in solar atmospheric heating.

Magnetic Evolution of Carrier Doping and Spin Dynamics in Diluted Magnetic Semiconductors (Ba,Na)(Zn,Mn)2As2

The investigation of novel diluted magnetic semiconductors (DMSs) provides a promising platform for studying magnetism and transport characteristics, with significant implications for spintronics. DMSs based on BaZn2As2 are particularly noteworthy due to their high Curie temperature (TC) of 260 K, diverse magnetic states, and potential for multilayer heterojunctions. This study investigates the magnetic evolution of carrier doping and spin dynamics in the asperomagnet (Ba,Na)(Zn,Mn)2As2, utilizing a combination of magnetization measurements, ac susceptibility, and muon spin rotation (µSR). Key findings include the following: (1) lower transition temperatures and coercive forces in (Ba,Na)(Zn,Mn)2As2 compared to the ferromagnet (Ba,K)(Zn,Mn)2As2; (2) a dynamic fluctuation peak around the transition temperature observed in both the ac susceptibility and longitudinal field (LF) µSR; and (3) the coexistence of static and dynamic states at low temperatures, exhibiting spin-glass-like characteristics. This study, to the best of our knowledge, may represent the first investigation of asperomagnetic order utilizing µSR techniques. It enhances the understanding of magnetic interactions in BaZn2As2-based systems and provides valuable insights into the exploration of high TC DMSs.

Crystal growth and magnetic evolution of antiferromagnetic topological insulator Zn-doped MnBi2Te4

Crystal growth and magnetic evolution of antiferromagnetic topological insulator Zn-doped MnBi2Te4