Search Results (66)

Background/Objectives: Despite extensive research, the underlying causes of amyotrophic lateral sclerosis (ALS) remain unclear. This umbrella review aims to synthesize a vast body of evidence from advanced magnetic resonance imaging (MRI) studies of ALS, encompassing a wide range of neuroimaging techniques and patient cohorts. Methods: Following the PRISMA guidelines, we conducted an extensive search of four databases (PubMed, Scopus, Web of Science, and Embase) for articles published until 3 December 2024. Data extraction and quality assessment were independently performed using the AMSTAR2 tool. Results: This review included 18 studies that incorporated data from over 29,000 ALS patients. Structural MRI consistently showed gray matter atrophy in the motor and extra-motor regions, with significant white matter (WM) atrophy in the corticospinal tract and corpus callosum. Magnetic resonance spectroscopy revealed metabolic disruptions, including reduced N-acetylaspartate and elevated choline levels. Functional MRI studies have demonstrated altered brain activation patterns and functional connectivity, reflecting compensatory mechanisms and neurodegeneration. fMRI also demonstrated disrupted motor network connectivity and alterations in the default mode network. Diffusion MRI highlighted microstructural changes, particularly reduced fractional anisotropy in the WM tracts. Susceptibility-weighted imaging and quantitative susceptibility mapping revealed iron accumulation in the motor cortex and non-motor regions. Perfusion MRI indicated hypoperfusion in regions associated with cognitive impairment. Conclusions: Multiparametric MRI consistently highlights widespread structural, functional, and metabolic changes in ALS, reflecting neurodegeneration and compensatory mechanisms. Full article

In this research, an analysis of the thermomagnetic properties of a nanoscale spin-2 and spin-3/2 system is conducted. This system is modeled with as a quasi-spherical Ising-type nanoparticle with a diameter of 2 nm, in which atoms with spin-2 and spin-3/2 configured in body-centered cubic (BCC) lattices interact within their relevant nanostructures. To determine the thermomagnetic behaviors of the nanoparticle, numerical simulations using Monte Carlo techniques and thermal bath class algorithms are performed. The results exhibit the effects of exchange couplings ($J_1,J_2^{\prime }$), magnetocrystalline anisotropies ($D_{3/2}^{\prime },D_2^{\prime }$), and external magnetic fields ($h^{\prime }$) on the finite-temperature phase diagrams of magnetization ($M_T$), magnetic susceptibility (${\chi }_T$), and thermal energy ($k_B{T}^{\prime }$). The influences of the exchange, anisotropic, and external field parameters are clearly reflected in the compensation, hysteretic, and pseudocritical phenomena presented by the quasi-spherical nanoparticle. When the parameter reflecting ferromagnetic second-neighbor exchanges in the nanosphere ($J_2^{\prime }$) increases, for a given value of the external magnetic field, the compensation ($T_{comp}$) and pseudocritical ($T_{pc}$) temperatures increase. Similarly, in the ranges $0<J_2^{\prime }⩽4.5$ and $-15⩽h^{\prime }⩽15$ at a specific temperature, an increase in $J_2^{\prime }$ results in the appearance of exchange anisotropies (exchange bias) and and increased hysteresis loop areas in the nanomodel. Full article

The Mesoproterozoic (~1470 Ma) Wolf River batholith (WRB) is exposed over 6500 km², encompassing 11 plutons that crosscut the Archean Marshfield and Proterozoic Penokean terranes. As the WRB is the classically defined anorogenic batholith, to test this hypothesis, seven igneous phases were analyzed using anisotropy of magnetic susceptibility (AMS), as a proxy for magmatic flow during intrusion, and the samples recorded a sub-horizontal emplacement in six different orientations. Paleopoles from six of eight igneous samples preserve a wide variety of sub-vertical orientations with two reversed and four normal polarities. The synorogenic Baldwin Conglomerate is the youngest rock (<1460 Ga) associated with WRB. Magnetic fabrics are horizontal, but multidomain and paleopole signatures, where interpretable, are sub-vertical. The North American APWP places middle Laurentia at low-latitude during Geon 14, and all our paleopoles are sub-vertical, not sub-horizontal, again suggesting post-intrusion deformation. Moreover, the McCauley gneiss (1886 Ma; U-Pb zircon), Rib Mountain Quartzite (1750 Ma MDA; U-Pb zircon, n = 150), Dells of the Eau Claire rhyolite (1483 Ma; U-Pb zircon, 1469 Ma; monazites-in-garnet), and Baldwin conglomerate (1460 Ma MDA; U-Pb zircons, n = 150) are sub-vertical inliers (xenoliths) in the igneous suite; the Proterozoic Wausau turbidite (1850 Ma MDA; U-Pb zircon, n = 150) was intruded by the WRB and dips 25°W. Here, we present a reinterpretation of the WRB as a deformed synorogenic rather than an anorogenic intrusion. Full article

Experimental protocols based on Electron Paramagnetic Resonance (EPR) and Raman spectroscopy are presented for the investigation of the Fe(II) spin transition in Cu(II)-doped 1-D spin-crossover (SCO) nanoparticles of the type [Fe_1−xCu_x(NH₂trz)₃]Br₂ where x = 0.03 and 0.06 and NH₂trz = 4-amino-1, 2, 4-triazole. The resulting nanoparticles were characterized using Transmission Electron Microscopy (TEM), Infrared (IR) spectroscopy, and powder X-ray diffraction (p-XRD). Magnetic susceptibility measurements revealed a dependence on the scan rate, with critical temperatures and hysteresis widths varying accordingly. EPR spectroscopy provided insights into the doped nanoparticles’ structural changes and spin-state transitions. The Cu(II) dopants exhibited significant g-factor anisotropy and hyperfine structure, indicative of a distorted octahedral coordination. The EPR spectra indicated that the spin transition occurs in domains populated by ions of the same spin state. Cu(II) ions show different spectral characteristics depending on whether they are in high-spin or low-spin domains of Fe(II). Changes in Raman bands induced by laser power reveal structural and electronic rearrangements during the LS to HS transition. The findings provide insights into metal–ligand interactions and the molecular mechanisms underlying the SCO process. Full article

The Banyo area, located in the southern prolongation of the Mayo Nolti shear zone trend, belongs to the western Cameroon domain of the Neoproterozoic Central African Belt (NCAB). It is made of granitic rocks that intrude metamorphic banded rocks. Both are sometimes mylonitized. The pluton is dominantly of paramagnetic behavior, as shown by the hysteresis loops and the Fe-bearing silicates crystals are the susceptibility carriers. AMS ellipsoids are dominantly of oblate shape, pointing to the importance of flattening during pluton emplacement. The anisotropy degree of magnetic susceptibility values (≤1.20) characterize the magmatic fabric flow. The microstructural study of the granite reveals magmatic, sub-magmatic, solid-state and mylonitic deformations. Field and AMS fabrics show evidence of polyphase deformation (D₁–D₃). The D₁ phase is of flattening mechanism (flat-laying foliation). The D₂ phase points to sinistral ductile simple shear accommodating moderate to steep dipping and N-S- to NW-SE-oriented foliations in plutonic and country rocks and conjugated E-W mylonitic foliation in country rocks bearing sub-horizontal- to moderate-plunge mineral stretching lineation. The D₃ phase is of dextral ductile simple shear. σ- and δ-type kinematic markers in the pluton indicate sinistral top-to-south sense of shear movement, indicating a non-coaxial component of the tectonics. The magnetic fabrics of the pluton are parallel to those of the D₂ deformation phase of the study area. The transpressive D₂ and D₃ events correlate with the D₂ and D₃ phases of the Pan-African tectonic dated at 613–585 Ma and 585–540 Ma, respectively. The pluton, then, emplaced during regional sinistral D₂ deformation under transpressive regime. The emplacement of the NE Banyo granite took place as rock strips sheared in sinistral sense of shear movement. Full article

Transverse magnetic susceptibility is an excellent tool to study singularity points as anisotropy and switching fields in different bulk and nanostructured systems, as well as phase transitions. This technique has been carried out on polycrystalline Y-type hexaferrites, with compositions Ba_2−xSr_xCo₂Fe₁₂O₂₂, (0.0 ≤ x ≤ 2.0), and Ba_2−xSr_xZn₂Fe₁₂O₂₂, (1.3 ≤ x ≤ 1.7), promising candidates to exhibit multiferroic properties due to their noncollinear spin structure. In the Co₂Y system, different behavior is observed depending on the Sr substitution rate, with a secondary maximum observed for samples with x ≥ 1.0 and different shapes in the measurement temperature range analyzed. In the Zn₂Y system, several peaks related to the phase transitions that take place are observed, with certain variations depending on the degree of Ba substitution and the applied field in a more or less extended region around the ambient temperature. This type of measurement is a valuable tool to determine the bias field and temperature range of spin transitions. Full article

In this paper, we focus on the properties of local energy minima and energy barriers in immobilized dense clusters of magnetic nanoparticles. Understanding of these features is highly interesting both for the fundamental physics of disordered systems with long-range interparticle interaction and for numerous applications of modern ferrofluids consisting of such clusters. In particular, it is needed to predict the ac-susceptibility of these systems and their magnetization relaxation after a sudden change in the external field, because both processes occur via magnetization jumps over energy barriers that separate the energy minima. Due to the exponential increase in the corresponding jump time with barrier height ($t_{\mathrm{sw}}\sim \exp (\Delta E/kT)$), direct Langevin dynamics simulations of this process are not feasible. For this reason, we have developed efficient numerical methods both for finding as many energy minima as possible and for the reliable evaluation of energy barriers between them. Our results for the distribution of overlaps between the local energy minima imply that there is no spin-glass state in such clusters even when they consist of particles with a small anisotropy. Further, we show that the distributions of energy barrier heights are qualitatively different for clusters of particles with small, intermediate, and large anisotropies, which has important consequences for the magnetization dynamics of these systems. Full article

Magnetotelluric (MT) sounding is a geophysical technique widely utilized in mineral resource surveys, where conductivity and magnetic permeability serve as essential physical parameters for forward modeling and inversion. However, the effects of conductive anisotropy and non-zero magnetic susceptibility are usually ignored. In this study, we present a three-dimensional (3D) MT modeling algorithm using Coulomb-gauged electromagnetic potentials, incorporating a mixed nodal and edge-based finite element method capable of simulating MT responses for conductive anisotropic and magnetic anomalies. Subsequently, the algorithm’s accuracy was validated in two steps: first, it was compared with analytical solutions for a 1D magnetic model; then, a comparison was made with previously published numerical results for a 3D generalized conductive anisotropic model. The results of two tests show that the maximum relative error is below 0.5% for both models. Furthermore, representative models were computed to comprehensively analyze the responses of MT. The findings illustrate the relationship between anisotropic parameters and electric fields and emphasize the significance of considering the impact of magnetic susceptibility in magnetite-rich regions. Full article

The marine magnetotelluric (MMT) method is a significant tool extensively utilized in offshore studies, including the understanding of the Earth’s tectonics and hydrocarbon exploration. Conductive anisotropy and non-zero magnetic susceptibility are common phenomena observed in the Earth’s subsurface, and MMT forward modeling is the basis of practical inversion. However, numerical modeling that incorporates both conductive anisotropy and magnetic susceptibility has received limited attention. Moreover, both accuracy and efficiency are crucial in developing a 3D MMT modeling algorithm. Therefore, we developed a multi-level parallel MMT forward modeling algorithm that is capable of simultaneously modeling conductive and magnetic arbitrary anisotropic models using the vector finite element method based on the secondary field formula. The algorithm’s accuracy was validated through comparisons with previously published results for an arbitrary anisotropic model. The results show that the maximum relative error is below 2%, and the speedup reaches an impressive value of 552.41 when running with 2048 cores. Furthermore, the MMT responses of conductive anisotropy and magnetic susceptibility were comprehensively analyzed by several typical models. Our findings highlight the importance of considering magnetic susceptibility in magnetite-rich regions, particularly as the MMT responses may exhibit opposite responses for anomalies with lower resistivity and higher magnetic susceptibility compared with the surrounding rocks. Full article

We synthesized some SWCNTs films under different magnetic fields and temperatures in a magnetic field-assisted FC-CVD and obtained Raman spectra of the films. By analyzing the Raman spectra, it was concluded that the SWCNTs films had defects, and the relative content of m-SWCNTs in the SWCNTs films was obtained. The trajectory of m-SWCNTs was obtained by analyzing the motion behavior of m-SWCNTs flow in the field-assisted system, and a model was built to describe the relationship between the relative content of m-SWCNTs and magnetic fields. The axial magnetic susceptibility of m-SWCNTs as a parameter was obtained by fitting the experimental results and the model. This is the first time that the axial magnetic susceptibility of m-SWCNTs has been obtained. The result obtained at 1273 K is at least two orders of magnitude greater than the magnetic susceptibilities and anisotropies of purified m-SWCNTs at 300 K, indicating that the defects increase the Curie temperature and Curie constant of m-SWCNTs. This is consistent with the spin-polarized density functional theory, which predicts that m-SWCNTs with vacancies have local magnetic moments around the vacancies and exhibit ferro- or ferrimagnetism. Full article

The Qaidam Block, located at the northern Qinghai–Tibet Plateau, is a pivotal area in unraveling the closure time of the Kunlun Ocean basin which might have recorded the transformation process between the Proto-Tethys and Paleo-Tethys Ocean basins. However, the late Triassic position of the Qaidam Block remains enigmatic, largely due to the scarcity of paleomagnetic data essential for quantitatively determining its paleolatitude. The widespread presence of the Elashan formation, particularly along the southern periphery of the Qaidam block, presents good material for conducting paleomagnetic work. Nevertheless, the primary magnetic carriers preserved within the Elashan formation might be influenced by multiple tectonic thermal events, particularly those associated with collisions between southern blocks and the Qaidam Block. Here we present rock magnetism and magnetic fabrics studies to identify the content and composition of magnetic minerals within the Elashan formation. The rock magnetic and petrologic results show that the magnetic carriers in the samples from the Elashan formation are dominated by magnetite with a small amount of goethite, pyrrhotite, and hematite. The results of Anisotropy in Magnetic Susceptibility indicate that the south of the Longwalangku section might not be obviously influenced by the tectonic events. Our results also provided guidance for future paleomagnetic research, emphasizing the importance of conducting further sampling away from adjacent faults, particularly in the southern Longwalangku area. Full article

Octahedral nickel(II) complexes are among the simplest systems that exhibit zero-field splitting by having two unpaired electrons. For the purpose of clarifying the relationship between structure and zero-field splitting in a low-symmetric system, distorted octahedral nickel(II) complexes were prepared with a tetradentate ligand, 2-[bis(2-methoxyethyl)aminomethyl]-4-nitrophenolate(1−) [(onp)⁻]. The complex [Ni(onp)(dmso)(H₂O)][BPh₄]·2dmso (1) (dmso = dimethyl sulfoxide) was characterized as a bulk sample by IR, elemental analysis, mass spectrometry, electronic spectra, and magnetic properties. The powder electronic spectral data were analyzed based on the angular overlap model to conclude that the spectra were typical of D₄-symmetric octahedral coordination geometry with a weak axial ligand field. Simultaneous analysis of the temperature-dependent susceptibility and field-dependent magnetization data yielded the positive axial zero-field splitting parameter D (H = g_uβS_uH_u + D[S_z² − S(S + 1)/3]), which was consistent with the weak axial ligand field. Single-crystal X-ray analysis revealed the crystal structures of [Ni(onp)(dmso)(H₂O)][BPh₄]·dmso (2) and [Ni(onp)(dmf)₂][BPh₄] (3) (dmf = N,N-dimethylformamide). The density functional theory (DFT) computations based on the crystal structures indicated the D₄-symmetric octahedral coordination geometries with weak axial ligand fields. This study also showed the importance of considering g-anisotropy in magnetic analysis, even if g-anisotropy is small. Full article

In this paper, we have synthesized the information derived from more than 20 papers and PhD theses on the anisotropy of the magnetic susceptibility (AMS) of 19 Variscan granite plutons, spanning the period between 320 Ma and 296 Ma. The AMS data are obtained from 876 sampling sites with more than 7080 AMS measurements and a re-interpretation is proposed. The studied granites exhibit a magnetic susceptibility (Km) ranging from 30 to 10,436 × 10⁻⁶ SI units. Most granites typically exhibit Km values below 1000 × 10⁻⁶ SI, indicative of paramagnetic behavior. Biotite serves as the main carrier of iron (Fe), emphasizing the reduced conditions prevalent during the formation of granite melts in the Variscan orogeny. The AMS fabrics of the studied granite plutons record the magma strain, expressing the chronologic evolution of the stress field during the orogeny. This chronologic approach highlights the magmatic events between around 330 and 315 Ma, occurring in an extensional regime, in which the Borralha pluton is an example of a suite that recorded this extensional AMS fabric. Plutons with ages between 315 and 305 Ma show AMS fabrics, pointing out their emplacement in a compressional tectonic regime related to the Variscan collision. The plutons, younger than 305 Ma, record AMS fabrics indicating that the tectonic setting for emplacement changes from a wrench regime to an extensional one at the end of the collision stage. This is evident as there is a chronological overlap between the granites that exhibit AMS fabrics indicating extension and the ones that have AMS fabrics indicating a wrench regime. Full article

The hexacoordinate Co(II) complex [Co(neo)₂(cin)][BPh₄]·½Me₂CO (1·½Me₂CO) containing trans-cinnamic acid (Hcin) and neocuproine (neo) was prepared. The compound 1·½Me₂CO was characterized via single-crystal X-ray analysis, FT-IR spectroscopy, and magnetic measurements. The coordination polyhedron of the complex cation adopts a deformed octahedron shape, and cinnamate exhibits a bidentate mode of coordination, which is unusual for mononuclear Co(II) cinnamate complexes. The analysis of DC magnetic measurements with zero-field splitting (ZFS) spin Hamiltonian revealed large magnetic anisotropy defined by the axial ZFS parameter D = +53.2 cm⁻¹. AC susceptibility measurements revealed the slow relaxation of magnetization under the applied field; thus, 1·½Me₂CO behaves as a field-induced single-molecule magnet. The analysis of magnetic properties was also supported by CASSCF/NEVPT2 calculations. Full article

Co₄₀Fe₄₀B₁₀Dy₁₀ thin films, with thicknesses varying between 10 nm and 50 nm, were grown on a Si(100) substrate. Subsequently, they underwent a 1 h annealing process in an Ar atmosphere at temperatures of 100 °C, 200 °C, and 300 °C. The oxide characteristic peaks of Dy₂O₃(440), Co₂O₃(422), and Co₂O₃(511) were revealed by X-ray diffraction (XRD). The low-frequency alternating current magnetic susceptibility (χ_ac) decreases with frequency. Due to thickness and the anisotropy of the magnetic crystal, the maximum χ_ac and saturation magnetization values rise with thicknesses and annealing temperatures. As the thickness and heat treatment temperature rise, the values for resistivity and sheet resistance tend to fall. The results of atomic force microscopy (AFM) and magnetic force microscopy (MFM) show that average roughness (Ra) lowers as the annealing temperature increases, and the distribution of strip-like magnetic domain becomes more visible. As thickness and annealing temperature increase, there is a corresponding rise in surface energy. Nano-indentation testing shows that hardness initially decreases from 10 nm to 40 nm, followed by an increase at 50 nm. Notably, annealing at 300 °C leads to a significant hardening effect, marking the highest level of hardness observed. Young’s modulus increased as thicknesses and annealing temperatures increased. The magnetic, electric, and adhesive characteristics of CoFeBDy films are highly dependent on surface roughness at various annealing temperatures. Full article