Magnetic Susceptibility Properties Research Articles

Exploration of a New α-T3 System for Electronic Heat Capacity and Pauli Magnetic Susceptibility Properties via the Kane-Mele and Hubbard Model

Exploration of a New α-T₃ System for Electronic Heat Capacity and Pauli Magnetic Susceptibility Properties via the Kane-Mele and Hubbard Model

Single-domain structure of Fe3O4 nanoparticles encapsulation by magnetic surfactant M(AOT)2 (M=Co, Ni)

Investigating the magnetic nanoparticle size and the effective magnetic interactions that form the magnetic domain can lead us to nanoparticles with targeted applications, such as targeted drug delivery and higher resolution MRI imaging. In this study magnetic susceptibility and coercive field properties, and the structure size range of single-domain magnetic capsules with high magnetization were obtained by structural analysis of volumetric DLS properties. In this regard, the role of exchange, anisotropy, and magnetostatic interaction was investigated in the structure of a magnetic capsule containing Fe3O4 nanoparticles (MCap-NPs). The stable capsules were synthesized in an emulsion solution with magnetic surfactants M(AOT)2 (M = Co, Ni). Vibrating Sample Magnetometer (VSM) and capsule relative volume (CRV) of Dynamic Light Scattering (DLS) were used to determine the magnetic properties of the single-domain (SD) structure. The produced emulsion samples were found to have superparamagnetic properties property with saturation magnetization in the range of 2–6 × 10−3emu/g for NiCap-NPs, and 5-13 × 10−3emu/g for CoCap-NPs. The results show that nanoparticles have the most significant effect on magnetization. The coercive field, the anisotropy energy values, and the SD of M(AOT)2 were determined using magnetic susceptibility distribution. The outcome results show that the surface of the magnetic capsule plays an essential role in forming a single-domain structure. It was also found that the saturation magnetization of the samples in the emulsion solution is proportional to the nanoparticle density and not to the mass of nanoparticles. All produced samples have distinct peaks in CRV versus capsule size, and each peak follows a log-normal distribution. For both samples, except for the samples with molar ratios ω of 23 (Co3 and Ni4 samples), the positions of the second and third relative volume peaks were constant at 269 ± 3 nm and 424±6 nm, respectively. The behavior of the CRV function normalized to the peak size showed a proportionality between the coercive field and the CRV.

Central Vein Sign and Paramagnetic Rim Lesions: Susceptibility Changes in Brain Tissues and Their Implications for the Study of Multiple Sclerosis Pathology.

Multiple sclerosis (MS) is the most common acquired inflammatory and demyelinating disease in adults. The conventional diagnostic of MS and the follow-up of inflammatory activity is based on the detection of hyperintense foci in T2 and fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) and lesions with brain-blood barrier (BBB) disruption in the central nervous system (CNS) parenchyma. However, T2/FLAIR hyperintense lesions are not specific to MS and the MS pathology and inflammatory processes go far beyond focal lesions and can be independent of BBB disruption. MRI techniques based on the magnetic susceptibility properties of the tissue, such as T2*, susceptibility-weighted images (SWI), and quantitative susceptibility mapping (QSM) offer tools for advanced MS diagnostic, follow-up, and the assessment of more detailed features of MS dynamic pathology. Susceptibility-weighted techniques are sensitive to the paramagnetic components of biological tissues, such as deoxyhemoglobin. This capability enables the visualization of brain parenchymal veins. Consequently, it presents an opportunity to identify veins within the core of multiple sclerosis (MS) lesions, thereby affirming their venocentric characteristics. This advancement significantly enhances the accuracy of the differential diagnostic process. Another important paramagnetic component in biological tissues is iron. In MS, the dynamic trafficking of iron between different cells, such as oligodendrocytes, astrocytes, and microglia, enables the study of different stages of demyelination and remyelination. Furthermore, the accumulation of iron in activated microglia serves as an indicator of latent inflammatory activity in chronic MS lesions, termed paramagnetic rim lesions (PRLs). PRLs have been correlated with disease progression and degenerative processes, underscoring their significance in MS pathology. This review will elucidate the underlying physical principles of magnetic susceptibility and their implications for the formation and interpretation of T2*, SWI, and QSM sequences. Additionally, it will explore their applications in multiple sclerosis (MS), particularly in detecting the central vein sign (CVS) and PRLs, and assessing iron metabolism. Furthermore, the review will discuss their role in advancing early and precise MS diagnosis and prognostic evaluation, as well as their utility in studying chronic active inflammation and degenerative processes.

Resilience of the Aurivillius structure upon La and Cr doping in a Bi5Ti3FeO15 multiferroic.

Combining the experimental techniques of high-resolution X-ray diffraction, magnetometry, specific heat measurement, and X-ray photoelectron, Raman and dielectric spectroscopy techniques, we have studied the influence of La and Cr doping on the crystal structure and magnetism of the room temperature Aurivillius multiferroic Bi5Ti3FeO15 by investigating the physical properties of (Bi4La)Ti3FeO15 and Bi5Ti3 (Fe0.5Cr0.5)O15. The parent (Bi5Ti3FeO15) and the doped ((Bi4La)Ti3FeO15 and Bi5Ti3(Fe0.5Cr0.5)O15) compounds crystallize in the A21am space group, which is confirmed through our analysis of high-resolution synchrotron X-ray diffraction data obtained on phase-pure polycrystalline powders. We determined the oxidation states of the metal atoms in the studied compounds as Fe3+, Ti4+, Cr3+, and La3+ through the analysis of X-ray photoelectron spectroscopy data. The magnetic susceptibilities of the three compounds are marked by the absence of a long-range ordered ground state, but dominated by superparamagnetic clusters with dominant antiferromagnetic interactions. This signature of short-range magnetism is also seen in specific heat as a low temperature enhancement which is suppressed upon the application of external magnetic fields up to 8 T. Our dielectric spectroscopy experiments showed that the three studied compounds display similar features in the dielectric constant measured as a function of frequency. However, upon doping La at the Bi site, the width of the ferroelectric hysteresis loop increases for (Bi4La)Ti3FeO15 compared to that of the parent compound Bi5Ti3FeO15, and with Cr doping, Bi5Ti3(Fe0.5Cr0.5)O15 becomes a leaky dielectric. The resilience of the Aurivillius crystal structure towards doping of La at the Bi site and Cr at the Fe site is clearly seen in the bulk properties of magnetic susceptibility, specific heat and the average crystal structure. The relevance of changes in the local structure is evident from our Raman spectroscopy and X-ray pair distribution function studies.

The evolution of penta-graphene thermoelectrics: External fields as a key enabler for High-Performance devices

The tight-binding model is used in this study to examine the electronic and thermal properties of penta-Graphene (PG). To analyze these properties, approaches including the Kubo formula, linear response theory, and Green's function method are applied. The obtained numerical results show that by introducing bias voltage U, external magnetic field Π, and electron doping μ, significant modifications in electrical conductivity, magnetic susceptibility, and thermoelectric properties including power factor PF(T), Seebeck coefficients S(T), and figure of merit ZT(T) are observed. The band structure and density of states (DOS) of PG structure can be significantly altered by applying a bias voltage or an external magnetic field. The wide band gap of PG exhibited a marked reduction with the application of these external fields, displaying greater sensitivity to Π compared to U. Thermal properties of PG, including electrical conductivity σ(T), exhibit a peak as a function of temperature, which its peak position depends on the external fields and μ. Below the peak, σ(T) increases significantly with increasing external fields and μ, due to the reduced band gap and increased number of excited charge carriers, respectively. σ(T) demonstrates greater sensitivity to μ compared to Π, and both parameters have a more pronounced effect than bias voltage U. The magnetic field and bias voltage shift the peak position of the power factor PF(T) in opposite directions. Through tuning of the external fields, which alters the electronic structure of PG, the ZT(T) can be enhanced and its rate of increase is more dependent on bias voltage than on magnetic field.

Constitution, physical properties and thermodynamic modeling of the Hf-Mn system

The Hf-Mn system is of a long-time interest due to the intermetallic Laves phase HfMn2, a hydrogen storage material. Although this system has been experimentally investigated by several authors and critical reviews and thermodynamic modelling have been performed, there is still a lack of reliable information, particularly as the phase "HfMn" (sometimes labelled as "Hf3Mn2" or "Hf2Mn") is suspected to be oxygen stabilized. This work includes a thorough investigation of the Hf-Mn phase equilibria employing diffusion zones, thermal analysis, powder and single crystal X-ray analyses, analytical electron microscopy as well as physical property studies of the Laves phase (magnetic susceptibility, specific heat, electrical resistivity and mechanical properties). The phase near “HfMn” was shown (TEM, WDX electron microprobe data, X-ray single crystal analysis) to be an oxygen stabilized phase with the formula Hf3+xMn3−xO1−y (defect η-W3Fe3C type). Properties such as magnetic susceptibility/magnetization; 2–300 K, specific heat (2–1100 K), electrical resistivity (2–300 K) classify HfMn2 as a metallic spin-fluctuation system with itinerant paramagnetism, originating from 3d states at Mn-sites and local moment paramagnetism of antisite Mn-atoms at Hf-sites. Mechanical properties (elastic moduli from density functional theory (DFT) and nanoindentation as well as hardness) group the Laves phase among rather hard and brittle intermetallics. DFT modeling revealed that Hf3+xMn3−x is thermodynamically unstable, but significant gains in enthalpy of formation arise from the inclusion of oxygen atoms, stabilizing the η phase. All phase diagram and DFT data together with the former literature information were used for the thermodynamic CALPHAD-type modelling of the Hf-Mn system.

The influence of anionic surfactant (SDS) on the optical, magnetic and capacitive properties of NiO nanocrystals via gas-liquid diffusion synthesis

A facile gas–liquid diffusion route with magnetic stirring was used for the preparation of black fungus-like NiO nanostructure with the assistance of SDS surfactant. The NiO obtained without addition of surfactant was used in the control test. The structure, composition and morphology of NiO nanocrystals were characterized by various methods including XRD, Raman, SEM, HRTEM, BET and XPS techniques. The optical properties were analyzed with UV–Vis DRS. The contact angle measurement and vibrating sample magnetometer were used to investigate surface wettability and magnetic properties respectively. The electrochemical behavior of two NiO samples was studied by CV and GCD tests. The characterization and test results showed that compared with surfactant-free NiO sample, the prepared NiO sample using SDS surfactant as template agent exhibited specific morphology and higher surface area, better optical properties, magnetic susceptibility and electrochemical properties.

Magnetic properties and magnetocaloric effect of a metallic triangular lattice antiferromagnetic DyAl2Ge2 single crystal

We report the synthesis, magnetic susceptibility, magnetization, electrical resistivity, heat capacity, and magnetocaloric properties of the metallic triangular lattice antiferromagnetic DyAl2Ge2 single crystal. High-quality rare-earth intermetallic compound DyAl2Ge2 single crystals were synthesized by the metallic flux method. DyAl2Ge2 crystallizes in a trigonal CaAl2Si2-type structure with Dy atoms forming a triangular lattice in the ab plane. The paramagnetic-antiferromagnetic transition occurs at 8 K, as determined by temperature dependencies of magnetic susceptibility and heat capacity. No observable hysteresis was found in the field-induced antiferromagnetic to the ferromagnetic metamagnetic transition of DyAl2Ge2. The electrical resistivity shows an overall metallic behavior with an upturn at the ordering temperature. For a magnetic field change of 0–70 kOe, the maximum magnetic-entropy change is −14.2 J kg−1 K−1 at 11 K and the relative cooling power is 327 J kg−1 with the applied magnetic field along the ab plane.

Structural and magnetic properties of superconductive YFeSb1.2 compound

The structural and magnetic analysis of the YFeSb[Formula: see text] compound synthesized by the solid-state reaction method was observed. At room temperature, the compound exhibits the ThCr2Si2-type structure with the space group of [Formula: see text]. Low-field DC magnetic susceptibility property of the YFeSb[Formula: see text] compound has been examined. An obvious oscillation of the remanent magnetization, [Formula: see text] with temperature was observed. The YFeSb[Formula: see text] compound exhibits large irreversibility at low fields below the coercivity fields due to freezing spins at low temperatures. At higher temperatures, the susceptibility obeys perfectly to modified Curie–Weiss behavior. Each magnetic ion on a microscopic scale and each magnetic cluster on a nanoscale experience reveal a local random anisotropy.

High angular resolution susceptibility imaging and estimation of fiber orientation distribution functions in primate brain

Uncovering brain-tissue microstructure including axonal characteristics is a major neuroimaging research focus. Within this scope, anisotropic properties of magnetic susceptibility in white matter have been successfully employed to estimate primary axonal trajectories using mono-tensorial models. However, anisotropic susceptibility has not yet been considered for modeling more complex fiber structures within a voxel, such as intersecting bundles, or an estimation of orientation distribution functions (ODFs). This information is routinely obtained by high angular resolution diffusion imaging (HARDI) techniques. In applications to fixed tissue, however, diffusion-weighted imaging suffers from an inherently low signal-to-noise ratio and limited spatial resolution, leading to high demands on the performance of the gradient system in order to mitigate these limitations. In the current work, high angular resolution susceptibility imaging (HARSI) is proposed as a novel, phase-based methodology to estimate ODFs. A multiple gradient-echo dataset was acquired in an entire fixed chimpanzee brain at 61 orientations by reorienting the specimen in the magnetic field. The constant solid angle method was adapted for estimating phase-based ODFs. HARDI data were also acquired for comparison. HARSI yielded information on whole-brain fiber architecture, including identification of peaks of multiple bundles that resembled features of the HARDI results. Distinct differences between both methods suggest that susceptibility properties may offer complementary microstructural information. These proof-of-concept results indicate a potential to study the axonal organization in post-mortem primate and human brain at high resolution.

Cerebral oxygen metabolism from MRI susceptibility

This article provides an overview of MRI methods exploiting magnetic susceptibility properties of blood to assess cerebral oxygen metabolism, including the tissue oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen (CMRO2). The first section is devoted to describing blood magnetic susceptibility and its effect on the MRI signal. Blood circulating in the vasculature can have diamagnetic (oxyhemoglobin) or paramagnetic properties (deoxyhemoglobin). The overall balance between oxygenated and deoxygenated hemoglobin determines the induced magnetic field which, in turn, modulates the transverse relaxation decay of the MRI signal via additional phase accumulation. The following sections of this review then illustrate the principles underpinning susceptibility-based techniques for quantifying OEF and CMRO2. Here, it is detailed whether these techniques provide global (OxFlow) or local (Quantitative Susceptibility Mapping - QSM, calibrated BOLD - cBOLD, quantitative BOLD - qBOLD, QSM+qBOLD) measurements of OEF or CMRO2, and what signal components (magnitude or phase) and tissue pools they consider (intravascular or extravascular). Validations studies and potential limitations of each method are also described. The latter include (but are not limited to) challenges in the experimental setup, the accuracy of signal modeling, and assumptions on the measured signal. The last section outlines the clinical uses of these techniques in healthy aging and neurodegenerative diseases and contextualizes these reports relative to results from gold-standard PET.

Magnetocaloric effect, magnetic susceptibility, heat capacity and optical properties of wedge-shaped quantum dots

Magnetocaloric effect, magnetic susceptibility, heat capacity and optical properties of wedge-shaped quantum dots

Hydrothermal Alteration Zones’ Magnetic Susceptibility Footprints and 3D Model of Iron Oxide-Copper-Gold (IOCG) Mineralization, Carajás Mineral Province, Brazil

Brownfield areas are important targets of exploration; however, the extensive drilling present in these areas has not fully exploited their prospective potential. The appropriate use of drill hole cores in these areas can play an important role in deep exploration. We present a case study of iron oxide-copper-gold (IOCG) Furnas Southeast deposit, located in the Carajás Mineral Province, Brazil. This deposit has disseminated chalcopyrite, bornite and gold mineralization associated with a silicic (Si), potassic (K), calcic (Na), sodic-calcic (Na-Ca) hydrothermal alteration, and intense iron metasomatism with massive magnetite (Fe) alteration. Petrophysical hand-held equipment measurements were carried out on drill core samples with the purpose of studying the potential roles that magnetic susceptibility properties can play in high-grade mineralization. The results indicate that the geological complexity of the IOCG deposit is readily reflected in the extensive variation of the measurements. The statistical analysis shows how the detailed characterization of this physical property carried out for this mineral association could effectively define and describe ore, and the magnetic susceptibility footprints of hydrothermal alteration zones. Furthermore, we were able to perform a magnetic susceptibility 3D modeling of diamagnetic, paramagnetic, and ferrimagnetic responses strictly correlated with known orebody. Thus, petrophysical analyses can form a quantitative geological criterion for ore delineation.

An astronomical age-depth model and reconstruction of moisture availability in the sediments of Lake Chalco, central Mexico, using borehole logging data

Understanding the moisture history of low latitudes from the most recent glacial period of the latest Pleistocene to post-glacial warmth in continental tropical regions is hampered by the lack of continuous time series. We conducted downhole spectral gamma (γ) ray and magnetic susceptibility logs over 300 m of lacustrine deposits of Lake Chalco (Mexico City) to reconstruct an age-depth model using an astronomical and correlative approach, and to reconstruct long-term moisture availability. Our results suggest that the Lake Chalco sediments contain several rhythmic alternations with a quasi-cyclic pattern comparable to the Pleistocene benthic stack. This allows us to calculate a time span of about 500,000 years for this sediment deposition. We developed proxies for moisture, detrital input, and salinity, all based on the physical properties of γ-ray spectroscopy and magnetic susceptibility. Our results indicate that Lake Chalco formed during Marine Isotope Stage 13 (MIS13) and the lake level gradually increased over time until the interglacial MIS9. Moisture content is generally higher during interglacials than during glacials. However, two periods, namely MIS6 and MIS4, have higher moisture contents. We developed a model by comparing the obtained moisture proxy with climatic drivers, to understand how different climate systems drove effective moisture availability in the Chalco sub-basin over the past 500,000 years. Carbon dioxide, eccentricity, and precession are all key drivers of the moisture content of Lake Chalco over the past 500,000 years.

Geochemical fingerprinting and magnetic susceptibility to unravel the heterogeneous composition of urban soils

The typically high heterogeneity of urban soil properties challenges their characterization and interpretation. The objective of this study was to investigate if proximally sensed volume-specific magnetic susceptibility and/or geochemical soil properties can uncover differences in anthropogenic, lithogenic and pedological contributions in, and between, urban soils. We also tested if volume-specific magnetic susceptibility can predict heavy metal enrichment. Data on 29 soil properties of 103 soil horizons from 16 soils from Ghent, Belgium, were analyzed by factor analysis. A correlation analysis, and in-depth analysis of five contrasting urban soils supplemented insights gained from the factor analysis.The factor analysis extracted four factors: 29.2 % of the soil property variability was attributed to fossil fuel combustion and industrial processes, with high (>0.80) loadings for S, organic carbon, magnetic susceptibility, and Zn. Furthermore, 26.0 % of the variability was linked to parent material differences, with high loadings (>0.80) for K, Rb and Ti. In absence of geogenic carbonates, increased soil alkalinity due to anthropogenic input of CaCO3 explained 17.0 % of the variability. Lastly, 4.7 % of the variability resulted from variable Zr contents by local geology. Elemental analysis by XRF, possibly combined with magnetic susceptibility measurements, helped to explain lateral or vertical differences related to (1) the nature of anthropogenic influence, for instance burning (e.g., by the S and Zn content) or the incorporation of building rubble (e.g., by the Ca content); (2) the particle size distribution (e.g., by the K, Rb or Ti content); (3) lithology (e.g., by the Zr content); or (4) pedology, such as organic matter build-up (e.g., by the S content) or leaching of alkalis (e.g., by the Ca content). Even though artifacts and soil translocation were common in the studied soils, volume-specific soil magnetic susceptibility measured on fine earth predicted the total heavy metal pollution loading index well (Pearson correlation = 0.85).

Magnetic Susceptibility Properties of Portland Cement

The raw materials for making cement consist of raw materials and auxiliary materials where the raw materials consist of Limestone (CaO) (± 80 %), Silica (SiO2) (± 10 %), Clay (Al2O3) (± 8 %), and Iron Sand (Fe2O3) (± 2%) while the auxiliary materials consist of Gypsum (Ca(SO4).2H2O), Pozzolan and Limestone (High Grade). The purpose of this study was to analyze the mineral content contained in iron sand (Fe2O3) used in cement mixtures. To see the mineral content in this cement, can use the magnetic method, one of which is the susceptibility method which is also assisted by the extraction method on cement to purify the iron sand contained in the cement later. The tool used is a Magnetic susceptibility meter type MS2B and extracted using strong and weak magnets 10 times. The extraction results with weak and strong magnets were obtained from 0.011759 gr to 0.35648 gr from 100 gr cement. Sensitivity test was carried out on cement samples with values ranging from 41.27 x 10-8 m3/kg to 44.2 x 10-8 m3/kg.

Negative permittivity and negative magnetic susceptibility of polypyrrole nanorings/carbon nanotubes multi-dimensional metacomposites in the radiowave frequency range

Metacomposites with negative electromagnetic properties are promising candidates for thin-film capacitors, wearable cloaks, and electromagnetic wave attenuation. In contrast to the complicated preparation procedures of traditional structural metamaterials, a two-dimensional (2D) polypyrrole nanoring (PPy NR) was constructed employing a facile soft template method. Negative permittivity and negative magnetic susceptibility were simultaneously observed in two-dimensional PPy loop structure and carbon nanotube (MWCNT)/PPy NR multi-dimensional composite materials, these properties exhibited significant dependence on the microstructures. The two-dimensional loop structure that contributed to the negative magnetic susceptibility could be conveniently adjusted through the morphology of the soft template. The conductive networks formed by PPy NRs and MWCNTs appeared to promote the apparent negative permittivity as well as negative electromagnetic properties within 100 MHz-1 GHz. The study of the structural design not only provided a novel approach for the realization of negative permittivity, but also offered a new design paradigm for negative magnetic susceptibility metacomposites. • PPy NRs with 2D loop-shaped microstructure were constructed employing a facile soft template method. • The 2D loop structure was conducive to the generation of negative permittivity and negative magnetic susceptibility due to their innate character of possessing many conductive loops. • Simultaneous negative permittivity and negative magnetic susceptibility properties were observed.

Distinct brain iron profiles associated with logopenic progressive aphasia and posterior cortical atrophy

Quantitative susceptibility mapping (QSM) can detect iron distribution in the brain by estimating local tissue magnetic susceptibility properties at every voxel. Iron deposition patterns are well studied in typical Alzheimer’s disease (tAD), but little is known about these patterns in atypical clinical presentations of AD such as logopenic progressive aphasia (LPA) and posterior cortical atrophy (PCA). Seventeen PCA patients and eight LPA patients were recruited by the Neurodegenerative Research Group at Mayo Clinic, Rochester, MN, and underwent MRI that included a five-echo gradient echo sequence for calculation of QSM. Mean QSM signal was extracted from gray and white matter for regions-of-interest across the brain using the Mayo Clinic Adult Lifespan Template. Bayesian hierarchical models were fit per-region and per-hemisphere to compare PCA, LPA, 63 healthy controls, and 20 tAD patients. Strong evidence (posterior probability > 0.99) was observed for greater susceptibility in the middle occipital gyrus and amygdala in both LPA and PCA, and in the right inferior parietal, inferior temporal, and angular gyri in PCA and the caudate and substantia nigra in LPA compared to controls. Moderate evidence for greater susceptibility (posterior probability > 0.90) was also observed in the inferior occipital gyrus, precuneus, putamen and entorhinal cortex in both LPA and PCA, along with superior frontal gyrus in PCA and inferior temporal gyri, insula and basal ganglia in LPA, when compared to controls. Between phenotypic comparisons, LPA had greater susceptibility in the caudate, hippocampus, and posterior cingulate compared to PCA, while PCA showed greater susceptibility in the right superior frontal and middle temporal gyri compared to LPA. Both LPA and PCA showed moderate and strong evidence for greater susceptibility than tAD, particularly in medial and lateral parietal regions, while tAD showed greater susceptibility in the hippocampus and basal ganglia. This study proposes the possibility of unique iron profiles existing between LPA and PCA within cortical and subcortical structures. These changes match well with the disease-related changes of the clinical phenotypes, suggesting that QSM could be an informative candidate marker to study iron deposition in these patients.

Effects of electron-phonon interaction and pressure on optical properties of wedge-shaped quantum dots

The energy levels and lattice vibrational modes in quantum dots (QDs) become discrete due to 3D quantum confinement. Therefore, the influence of electron-phonon (e-p) interaction on physical properties of QDs is an important subject to study. In this work, the effects of e-p interaction and pressure in a GaAs wedge-shaped (WS) quantum dot are considered. In first step, using the dielectric continuum model, the Hamiltonian of longitudinal optical (LO) phonons and the e-p interaction Hamiltonian are analytically derived. In the next step, we have studied the e-p effect on energy eigenvalues, magnetic susceptibility and optical properties of the WS quantum dot. We have also investigated the pressure effect on optical properties of the system in the presence of the e-p interaction. It is found that the polaronic energy shift reduces when the QD size increases. The magnetic susceptibility enhances with raising the QD size. The e-p effect on magnetic susceptibility is strong for smaller QD sizes. The absorption coefficient shows two peaks in the presence of the e-p interaction. The refractive index change enhances and moves to higher energies under the e-p interaction. We found that the pressure and e-p interaction, simultaneously, have important effects on absorption coefficient and refractive index changes.

Persisting correlation between electrical transport and magnetic dynamics in M-type hexaferrites

In this work, we present frequency-dependent magnetic susceptibility and dc electric transport properties of three different compositions of hexaferrite Ba1−xPbxFe12−yAlyO19 single crystals. We found a correlation between the activation energies of the dc electric transport and the ac magnetic susceptibility which persists over the whole studied range of aluminum substitution y = 0–3.3. This result is discussed in the context of charged magnetic domain walls, the pinning of which is determined by charge carriers activated across the transport gap. Our work points toward a general relaxation mechanism in ferrimagnetic semiconductors that directly affects the dynamic magnetic properties via electrical transport.