Magnetic Measurements Research Articles

Synthesis, Optical, and Magnetic Properties of the Mixed Chalcogenide Semiconductor Series Eu(II)2SiSexS4-x, Prepared via the Flux-Assisted Boron Chalcogen Mixture Method.

We report a detailed structural study of a series of five new quaternary Eu(II)-containing mixed chalcogenide phases, Eu2SiSe0.85S3.15, Eu2SiSe2.4S1.6, Eu2SiSe2.6S1.4, Eu2SiSe3.1S0.9, and Eu2SiSe4, synthesized using the flux-assisted boron chalcogen mixture (BCM) method. High-quality crystals were grown, and their crystal structures were determined by single-crystal X-ray diffraction. All members of the Eu2SiSexS4-x series crystallize in the monoclinic crystal system with space group P21/m, except Eu2SiSe4, which crystallizes in the P21 space group. The crystal structure of Eu2SiSexS4-x exhibits a complex three-dimensional network and is primarily composed of distorted trigonal prismatic EuQ6 polyhedra that are interconnected by SiQ4 tetrahedra. Polycrystalline powders were used for physical property measurements, including the magnetic susceptibility and UV-vis diffuse reflectance. Magnetic measurements indicated paramagnetic behavior with a slightly negative Weiss constant (θ = -13.54). The band gaps of the materials were determined from diffuse reflectance data, with optical band gaps estimated to be 2.04(2) eV, 1.98(2) eV, and 1.90(2) eV for Eu2SiSe0.85S3.15, Eu2SiSe2.6S1.4, and Eu2SiSe4, respectively. Band gap tuning was achieved by partially or fully replacing the S sites with Se.

A Record-High Cryogenic Magnetocaloric Effect Discovered in EuCl2 Compound.

Adiabatic demagnetization refrigeration (ADR) based on the magnetocaloric effect (MCE) is a promising technique to achieve cryogenic temperature. However, magnetic entropy change (ΔSM), the driving force of ADR, remains far below theoretical -ΔSM = nRln(2J + 1)/MW for most magnetic refrigerants. Here, we report giant MCE in orthorhombic EuCl2, where a ferromagnetic ground state with excellent single-ion behavior of Eu2+ and free spins has been demonstrated by combining ab initio calculations with Brillouin function analysis and magnetic measurements. Consequently, a record-high -ΔSM ∼ 74.6 J·kg-1·K-1 (1.8 K) at 5 T was experimentally achieved, approaching 96% of the theoretical limit (77.5 J·kg-1·K-1). At a lower field of 1 T, EuCl2 also achieves the highest-ever record of -ΔSM ∼ 36.8 J·kg-1·K-1. Further, direct quasi-adiabatic demagnetization measurements demonstrate that its large -ΔSM allows EuCl2 to maintain a long holding time at sub-Kelvin temperature (∼346 mK), surpassing all previously reported materials. These superior magnetocaloric performances position EuCl2 as an attractive cryogenic refrigerant.

Experimental Study on the Alternate Oil Displacement Mechanism of CO2 and Modified Water in Low-Permeability Oil Layers

Alternating carbon dioxide and water flooding can not only seal greenhouse gases, but also combine the advantages of water flooding and carbon dioxide flooding, and can well control mobility and stabilize the displacement front, thereby greatly improving the macro-replacing efficiency. In order to further improve the development effect of water–carbon dioxide alternating flooding, this paper, based on sufficient collection of the literature, research, and analysis, pre-uses modified water instead of water, and deeply explores and studies the impact of modified water–carbon dioxide alternating flooding on the improvement of development effect and the mechanism of enhancing oil recovery in low-permeability reservoirs. The main work completed is as follows: (1) A comparative experiment of multiple groups of sand-filled tubes with different displacement media, modified water concentrations, and injection plug sizes was conducted under the conditions of simulating reservoir formation temperature of 70 °C and formation pressure of 18 MPa, and the optimal scheme and injection parameters of alternating modified water and carbon dioxide flooding were rationally selected. The results show that the alternating flooding of modified water and carbon dioxide in low-permeability reservoirs can significantly improve the development effect. The optimal injection parameters are a formulation concentration of 0.3% and an injection method of alternating a 0.1 PV slug injection of carbon dioxide and modified water. (2) Using Berea cores instead of sand-fill tubes, a comparative experiment of alternating oil displacement using carbon dioxide and modified water was carried out under the same experimental conditions. Nuclear magnetic resonance measurements were performed on five of the cores to analyze the microscopic oil displacement mechanisms of different displacement media. The results show the following: nuclear magnetic resonance testing shows that carbon dioxide displacement can greatly improve the oil recovery efficiency in tiny pores (about 47.43%); alternating injection can further improve the oil recovery efficiency in tiny pores (about 70.6%); and modified water can improve the oil recovery efficiency in larger pores (about 56.47%).

The menopausal transition and multiple physiologic measures of early brain health in the Coronary Artery Risk Development in Young Adults study.

This study proposed to investigate the cross-sectional and longitudinal associations of menopausal status with physiologic brain magnetic resonance imaging measures. The sample included women from the Coronary Artery Risk Development in Young Adults study who self-reported their reproductive histories and participated in the brain magnetic resonance imaging substudies at the year 25 (n = 292) and year 30 (n = 258) follow-up examinations. Menopausal status was classified based on natural menstrual cycle regularity/cessation at both time points. Gray matter cerebrovascular reactivity (CVR) was calculated as mean percent change in blood oxygen level-dependent signals in activated voxels following a breath-hold challenge. Gray matter cerebral blood flow (CBF) was assessed using pseudo-continuous arterial spin labeling. Linear regression models were used to examine cross-sectional and longitudinal associations of menopausal status with gray matter CVR and CBF after adjustment for potential age-related covariates. Women were mean age 50 years at year 25; 37% were Black; and 46% were postmenopausal. Relative to premenopause or perimenopause, postmenopause was associated with lower gray matter CVR at year 30 cross-sectionally (1.86% vs 1.69%, P = 0.03, respectively) and longitudinally for women who were postmenopausal at both time points (-0.32% [95% CI, -0.63% to -0.02%]) after covariate adjustment. Mean CVR values were also lower for these women when compared with women who remained premenopausal or perimenopausal (1.71% compared with 2.04%, respectively). Menopausal status was unrelated to either concurrent or longitudinal gray matter CBF. These findings suggest that the ability of vessels to adapt in response to hypercapnia may be impaired during menopause, even within a relatively short time window.

Water Encapsulated [(Fe4Se4)Se4]6- Clusters in [Na6(H2O)18][Fe4Se8

[Na6(H2O)18][Fe4Se8] was synthesized using hydrothermal methods and characterized by single-crystal X-ray diffraction, 57Fe Mössbauer spectroscopy, magnetization, and muon spin resonance (μSR) measurements. The cubic crystal structure (space group I23, a = 11.785 Å, Z = 2) contains heterocubane-type clusters with Td symmetry. Four additional selenium atoms complete the tetrahedral coordination around the iron atoms, forming units. Notably, the selenide ligands do not interact with the sodium cations, as the Fe4Se86- cluster in [Na6(H2O)18][Fe4Se8] is exclusively surrounded by water molecules via weak Se···H-O hydrogen bonds. This is particularly remarkable given that [Fe4Q4] clusters are typically unstable in water. Quantum chemical calculations (DFT) confirm the crystal structure and improve the positions of the hydrogen atoms. 57Fe Mössbauer spectroscopy reveals that the spin ordering of the mixed-valence [Fe42.5+Se4]2+ cluster core mirrors the antiparallel spin arrangement found in analogous iron-sulfur clusters, such as , in protein-bound systems. An increase of the quadrupole splitting at low temperatures indicates changes of the orbital occupations. μSR Experiments show a reduction of the spin fluctuation frequency until the system becomes static at low temperatures, but no evidence of a S = 0 state above 2 K.

On detecting and characterizing planetary oceans in the solar system using a distance-based ensemble modelling approach: application to the Uranus system.

The discovery of Europa's subsurface ocean has spawned a strong desire by the planetary community to return and assess the ocean's habitability using the magnetic induction signal that Europa generates. NASA has since formulated and developed the Europa Clipper mission with that same goal, anticipating its arrival in the Jovian system in the early 2030s. In parallel, ESA has developed the JUpiter Icy moons Explorer mission to further investigate the interior of Ganymede and other Jovian moons, scheduled to arrive approximately one year later. As a result, extensive work has now been devoted to developing and refining methods to analyse magnetic induction measurements with the goal of characterizing oceans within icy moons, including those in the Neptune and Uranus systems, which are ideal laboratories for such investigations. We present one such method, involving a distance-based inverse and forward modelling approach that leverages self-consistent interior models used to infer ocean and ice-shell properties of various moons that respond inductively to the dynamic magnetic environments in which they reside. We demonstrate the method on a hypothetical ocean within Umbriel, showing the ocean thickness and conductivity constraints that can be inferred from a Monte Carlo error analysis using a three-flyby mission concept.This article is part of the theme issue 'Magnetometric remote sensing of Earth and planetary oceans'.

Using NMR linewidth broadening for magnetic characterization of micrometer-size particles in silicone matrix

Standard magnetization measurements on samples of small magnetic particles may generate conflicting results. We compare the mass magnetization of MgZn ferrite particles in a compressed bulk material and in dry powder and find that at low fields the values can differ by as much as 50%. We show here that embedding the particles in a silicone matrix and measuring the NMR linewidth in combination with simulations establishes a new method to evaluate the magnetization of the particles at different fields and temperatures. The NMR results agree with the direct magnetization measurements of the powder samples and the magnetization measurements of the particles embedded in silicone. This work is motivated, in part, by studies on using small magnetic particles as MRI temperature indicators, and we compare the effectiveness of these particles for low-field and high-field MRI thermometry.

Soft x-ray tomography using L1 regularization for MHD modes with limited sight lines in JT-60SA.

Soft x-ray (SX) tomography is a useful diagnostic in fusion research, and a multi-channel SX diagnostic will be installed in JT-60SA, the largest elongated tokamak in the world. However, in the SX diagnostic of JT-60SA, plasmas will be only viewed from the low field side and the upper side of plasmas; the sight lines are limited, which would be common in future devices as well as JT-60SA. This kind of limited sight lines is not preferred for SX tomography to investigate the spatial structure of magnetohydrodynamics (MHD) modes because inadequate information of plasmas makes artifacts in the reconstructed SX profiles. One of the solutions to reduce the artifacts is to employ L1 regularization, which gives the essential and sparse contributions [Kaptanoglu etal., Phys. Plasmas 30, 033906 (2023)]. In this study, as a first topic, the applicability of L1 regularization to reduce the artifacts in SX tomography with limited sight lines is investigated with traditional L2 regularization for a high beta scenario of JT-60SA where MHD modes would occur. Here, as a series of basis functions, the Fourier-Bessel series (FBS) is employed because FBS has the poloidal Fourier modes explicitly. A disadvantage of FBS is that the accurate equilibrium inside the last closed flux surface (LCFS) is needed; interior measurement such as the motional Stark effect measurement is required, which is not always available during a whole discharge. The second topic of this study is to investigate other appropriate basis functions to study the spatial structure of MHD modes in elongated tokamak plasmas. Here, we introduce Saito's Laplacian eigenfunction (LEF). Saito's LEF can be calculated if LCFS is given and the LEF is expected to show the explicit poloidal Fourier mode. Because the calculation of LCFS with magnetic measurements is a basic task of plasma operations, Saito's LEF may be used anytime. Our investigation showed that L1 regularization can strongly improve the SX tomography with the traditional L2 regularization having FBS/LEF and would be effective against other tomographic problems in fusion devices.

Crystal structure and magnetic properties of Fe doped BaTiO3 at morphotropic phase boundary

Ceramic compounds BaTi1-xFexO with x = 0 – 0.2 prepared by solid state reaction technique were studied using X-ray diffraction, Raman spectroscopy, and magnetometry methods focusing on the correlation between the structure and magnetic properties. Chemical doping with Fe ions leads to a concentration driven structural transformation from the single phase tetragonal (T-) structure to the hexagonal (H-) structure with a mixed structural state stable in the concentration range 0.06 <x ≤ 0.2. Increase in the Fe ions content causes a stabilization of weak ferromagnetic state driven by the exchange interactions Fe3+ – O – Fe3+ ions strongly dependent on the structural positions of the Fe ions. Increase of the dopant content above x = 0.08 leads to a decrease of the remnant magnetization which is mainly caused by a stabilization of Fe4+ ions as well as by the lattice defects associated with oxygen vacancies formed to keep electroneutrality of the compounds. The results of the structural and magnetization measurements allowed to itemize the type of exchange interactions between Fe ions residing different structural positions of the hexagonal lattice as well as to reveal structural instability of the T- and H- phases under ambient conditions and applied electric field which shows a possibility to control the structure and magnetic properties of the mixed compounds via external stimuli.

Magnetocaloric effect in geometrically frustrated GdInO[formula omitted]

We have investigated the magnetic and magnetocaloric properties of geometrically frustrated rare-earth indium oxide, GdInO3, by magnetization and heat capacity measurements. It is found that the spin moments of Gd3+ ion undergo a paramagnetic to antiferromagnetic transition below 2 K. At low-magnetic fields, the dc magnetic susceptibility exhibits a clear deviation from the Curie–Weiss (CW) law below 150 K due to the strong magnetic frustration. However, with increasing field strength, the magnetic frustration weakens and the susceptibility data follow the expected CW behavior down to 2 K. The effective paramagnetic moment of Gd3+ ion calculated from the CW fit (∼8μB/Gd) is very close to the theoretical value for S=7/2. The maximum values of magnetic entropy change and adiabatic temperature change for a field change of 0–7 T are found to be ∼21 J kg−1 K−1 (∼155 mJ cm−3 K−1) and ∼15 K, respectively, while the refrigeration capacity is found to be ∼188 J kg−1 for μ0H = 7 T. The large values of magnetocaloric parameters along with negligible hysteresis loss suggest that GdInO3 could be considered as a potential candidate for magnetic refrigeration at low temperature.

First Observation of the Complete Rotation Period of the Ultraslowly Rotating Magnetic O Star HD 54879

HD 54879 is the most recently discovered magnetic O-type star. Previous studies ruled out a rotation period shorter than 7 yr, implying that HD 54879 is the second most slowly rotating known magnetic O-type star. We report new high-resolution spectropolarimetric measurements of HD 54879, which confirm that a full stellar rotation cycle has been observed. We derive a stellar rotation period from the longitudinal magnetic field measurements of P=2562−58+63 days (about 7.02 yr). The radial velocity of HD 54879 has been stable over the last decade of observations. We explore equivalent widths and longitudinal magnetic fields calculated from lines of different elements, and conclude the atmosphere of HD 54879 is likely chemically homogeneous, with no strong evidence for chemical stratification or lateral abundance nonuniformities. We present the first detailed magnetic map of the star, with an average surface-magnetic-field strength of 2954 G, and a strength for the dipole component of 3939 G. There is a significant amount of magnetic energy in the quadrupole components of the field (23%). Thus, we find HD 54879 has a strong magnetic field with a significantly complex topology.

Study of the magnetoelastic phase transition in near equiatomic FeRh alloys through T-FORC analysis and neutron diffraction

Fe100-xRhx alloys with x ∼ 50 undergo a first-order magnetoelastic phase transition close to room temperature from the low-temperature antiferromagnetic (AFM) to the high-temperature ferromagnetic (FM) state. For Fe50Rh50, the AFM-FM-AFM transitions may occur involving various coexistent mechanisms. Although the Fe49Rh51 composition closely resembles the equiatomic counterpart, its first-order phase transition exhibits notable disparities, whose underlying process remains unexplained. We combined neutron thermo-diffraction and magnetization measurements to study the phase transformation in the two alloys. The Kolmogorov-Johnson-Mehl-Avrami (KJMA) model and temperature first-order reversal curve (T-FORC) analysis are applied to explore this matter. The techniques were applied to both alloys, Fe50Rh50 and Fe49Rh51, to use the former as reference to emphasize the distinct characteristics of the latter. The study highlights the defect-based growth hindering in Fe50Rh50 and the almost complete absence of it in Fe49Rh51, accompanied by a significant effect of the FM phase magnetostatic field. This work presents a new way to obtain detailed information from the T-FORCs by analyzing their T-derivative curves. This method indicates that the superposition of applied and magnetostatic fields causes the notable differences observed in alloys with such close atomic composition. It reveals and explains peculiar features of the Fe49Rh51 temperature-driven transition, such as the anomalous cross-over of the first-order reversal magnetization curves at low temperatures, that could pave the way to a deeper understanding of the mechanisms driving the magnetostructural phase transition in these alloys.

Holistic numerical simulation of a quenching process on a real-size multifilamentary superconducting coil

Superconductors play a crucial role in the advancement of high-field electromagnets. Unfortunately, their performance can be compromised by thermomagnetic instabilities, wherein the interplay of rapid magnetic and slow heat diffusion can result in catastrophic flux jumps, eventually leading to irreversible damage. This issue has long plagued high-Jc Nb3Sn wires at the core of high-field magnets. In this study, we introduce a large-scale GPU-optimized algorithm aimed at tackling the complex intertwined effects of electromagnetism, heating, and strain acting concomitantly during the quenching process of superconducting coils. We validate our model by conducting comparisons with magnetization measurements obtained from short multifilamentary Nb3Sn wires and further experimental tests conducted on solenoid coils while subject to ramping transport currents. Furthermore, leveraging our developed numerical algorithm, we unveil the dynamic propagation mechanisms underlying thermomagnetic instabilities (including flux jumps and quenches) within the coils. Remarkably, our findings reveal that the velocity field of flux jumps and quenches within the coil is correlated with the cumulated Joule heating over a time interval rather than solely being dependent on instantaneous Joule heating power or maximum temperature. These insights have the potential to optimize the design of next-generation superconducting magnets, thereby directly influencing a wide array of technologically relevant and multidisciplinary applications.

Magnetic properties of tire cord as a diagnostic parameter of car tires condition

This article presents the possibility of using the magnetic measurement method, which is an alternative method to shearography as a method of testing the condition of the cord of all-steel tires in order to determine the possibility of using the casing for the retreading process. It is an extension of the design and research work aimed at creating a prototype of a diagnostic device. As part of the activities, a prototype of the device and a version of the measuring head were developed, but a prototype of the algorithm of the measurement program was also created, which uses the physical foundations of non-destructive measurements of motor vehicle tires developed within the project. This study is related to the increasingly strict regulations and the intentions of the European Commission regarding the use of vehicles, which require an increase in the share of recycled materials, including tires. Therefore, there is a need to develop measurement methods that allow for the assessment of the quality of the casing while the used tires are still stored. This work presents the results of theoretical analyses of the possibility of using the magnetic field as a diagnostic parameter of the condition of tires

Characterization of a Mechanical Antenna Based on Rotating Permanent Magnets

Mechanical antennas with rotating permanent magnets are a relatively new type of transmitting antenna in low- and ultralow-frequency (LF/ULF) ranges. The perspectives of the applications are encouraging, especially in the field of non-destructive defectoscopy and communications through conductive media (underwater communications), which is reflected in the articles published in the last decade. This article describes the experimental setup, results, harmonic analysis, and simulation validation for two configurations of mechanical antennas with rotating NdFeB permanent magnets. The emphasis is placed on the known analytical equations, specifically on the matching of the measurement results with the analytical data as well as with the results given by the numerical analysis. Also, several means of measurement are used to validate the results through replicate testing. Through analytical analysis and the performed measurement, this article establishes the basics for designing mechanical antennas with rotating permanent magnets for the considered configurations based on a single static magnetic field measurement. Finally, we explore prospects for future research in this domain as well as the advantages and disadvantages compared to other types of LF/ULF antennas.

Structure and Mobility of the Lipid System in Mixtures of Ethylammonium Nitrate and Water: Magnetic Resonance Measurements and Molecular Dynamics Simulations

Structure and Mobility of the Lipid System in Mixtures of Ethylammonium Nitrate and Water: Magnetic Resonance Measurements and Molecular Dynamics Simulations

Synthesis, characterization, and bioactivity of Cu(II), Fe(II), Co(II), Ni(II), and Mn(II) complexes with benzilmonoximethiocarbohydrazide-O-methoxybenzaldehyde: experimental and computational insights.

In this study, a novel ligand, benzilmonoximethiocarbohydrazide-O-methoxybenzaldehyde (HBMToMB), was synthesized and subsequently complexed with Cu(II), Fe(II), Co(II), Ni(II), and Mn(II) ions. The metal complexes were comprehensively characterized using techniques such as NMR, IR, Mass Spectrometry, UV-Vis, elemental analysis (CHNS), and magnetic susceptibility measurements. The complexes exhibited superior antibacterial and antifungal activity compared to the free ligand. In addition, cytotoxicity was evaluated using the brine shrimp lethality bioassay, demonstrating significant activity. Computational studies, including molecular docking, DFT, and ADMET analysis, provided further insights into the compounds' binding affinities and electronic properties. These findings underscore the potential of these metal complexes as promising candidates for therapeutic applications, particularly in antimicrobial and anticancer therapies.

Magnetic properties of the RNiIn4 (R = Ce, Pr, Nd) series of intermetallic compounds grown by the metallic flux method

This work focuses on the synthesis, structural and magnetic characterization, and the effects of the Crystal Electric Field (CEF) of RNiIn4 (R = Ce, Pr, Nd) compounds. By using the metal flux technique, high-quality single crystals were obtained and analyzed X-ray diffraction and confirmed the formation of a single phase for all compounds and revealed their crystallization in a orthorhombic structure. Magnetic susceptibility measurements revealed antiferromagnetic in order ing temperatures (TN) at 4.02 K, 2.37 K and 4.06 for Ce, Pr, and Nd, respectively. Specific heat data corroborated these findings. The results indicate the easy axis of magnetization lies in the ab-plane for Ce and Nd, and along the c-axis for Pr.

Effect of carbon ion implantation on the superconducting properties of MgB2 bulks prepared by powder-in-sealed-tube method

We studied the effect of carbon (C) ion implantation on the microstructure and superconducting properties of bulk MgB2 prepared by the powder-in-sealed-tube (PIST) method. FESEM and TEM analysis indicate microstructural changes due to carbon ion implantation. DC magnetization measurements reveal a slight improvement of TC and small ΔTC values due to ion implantation. The JC(B) characteristics of implanted samples show a significant enhancement of JC compared with pristine MgB2 at 10 and 20 K. MgB2 samples implanted with 80 keV carbon ions with a dose of 2 × 1016 ions cm−2 show maximum enhancement in JC i.e., 2.07 × 105 A/cm2 at 5 T and 10 K. The flux pinning force density curves are theoretically analyzed using the Dew-Hughes model. The results reveal that significant enhancements in the flux pinning properties are contributed by the normal point defects caused by carbon ion implantation, which acts as a strong pinning center.

Measurements of the solar coronal magnetic field based on coronal seismology with propagating Alfvénic waves: forward modeling

Abstract Recent observations have demonstrated the capability of mapping the solar coronal magnetic field using the technique of coronal seismology based on the ubiquitous propagating Alfv'{e}nic/kink waves through imaging spectroscopy. We established a magnetohydrodynamic (MHD) model of a gravitationally stratified open magnetic flux tube, exciting kink waves propagating upwards along the tube. Forward modeling was performed to synthesize the Fe \textsc{xiii} 1074.7 and 1079.8 nm spectral line profiles, which were then used to determine the wave phase speed, plasma density, and magnetic field with seismology method. A comparison between the seismologically inferred results and the corresponding input values verifies the reliability of the seismology method. In addition, we also identified some factors that could lead to errors during magnetic field measurements. Our results may serve as a valuable reference for current and future coronal magnetic field measurements based on observations of propagating kink waves.