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Tuning the band gap is of utmost importance for the practicality of two-dimensional materials in the semiconductor industry. In this study, we investigate the ballistic transport and the tunneling magnetoresistance (TMR) properties within a modulated gap in a ferromagnetic/normal/ferromagnetic (F/N/F) phosphorene junction. The theoretical framework is established on a Dirac-like Hamiltonian, the transfer matrix method, and the Landauer-Büttiker formalism to characterize electron behavior and obtain transmittance, conductance and TMR. Our results reveal that a reduction in gap energy leads to an enhancement of conductance for both parallel and anti-parallel magnetization configurations. In contrast, a significant reduction and redshift in TMR have been observed. Notably, the application of an electrostatic field in a gapless phosphorene F/N/F junction induces a blueshift and a slight increase in TMR. Furthermore, we found that introducing an asymmetrically applied electrostatic field in this gapless junction results in a significant reduction and redshift in TMR. Additionally, intensifying the applied magnetic field leads to a substantial increase in TMR. These findings could be useful for designing and implementing practical applications that require precise control over the TMR properties of a phosphorene F/N/F junction with a modulated gap.

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Iron niobates, pure and substituted with copper (Fe1-xCuxNbO4 with x = 0-0.15), were prepared by the solid-state method and characterized by X-ray diffraction, Raman spectroscopy, and magnetic measurements. The results of the structural characterizations revealed the high solubility of Cu ions in the structure and better structural stability compared to the pure sample. The analysis of the magnetic properties showed that the antiferromagnetic-ferromagnetic transition was caused by the insertion of Cu2+ ions into the FeNbO4 structure. The pure FeNbO4 structure presented an antiferromagnetic ordering state, with a Néel temperature of approximately 36.81K. The increase in substitution promoted a change in the magnetic ordering, with the state passing to a weak ferromagnetic order with a transition temperature (Tc) higher than the ambient temperature. The origin of the ferromagnetic ordering could be attributed to the increase in super-exchange interactions between Fe/Cu ions in the Cu2+-O-Fe3+ chains and the formation of bound magnetic polarons in the oxygen vacancies.

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Magnetization-graded ferromagnetic nanostrips are proposed as potential prospects to channel spin waves. Here, a controlled reduction of the saturation magnetization enables the localization of the propagating magnetic excitations in the same way that light is controlled in an optical fiber with a varying refraction index. The theoretical approach is based on the dynamic matrix method, where the magnetic nanostrip is divided into small sub-strips. The dipolar and exchange interactions between sub-strips have been considered to reproduce the spin-wave dynamics of the magnonic fiber. The transition from one strip to an infinite thin film is presented for the Damon-Eshbach geometry, where the nature of the spin-wave modes is discussed. An in-depth analysis of the spin-wave transport as a function of the saturation magnetization profile is provided. It is predicted that it is feasible to induce a remarkable channeling of the spin waves along the zones with a reduced saturation magnetization, even when such a reduction is tiny. The results are compared with micromagnetic simulations, where a good agreement is observed between both methods. The findings have relevance for envisioned future spin-wave-based magnonic devices operating at the nanometer scale.

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In this paper, we theoretically investigate the stability of spin-wave solitons in Bose-Einstein condensates of repulsive magnons, confined by an inhomogeneous external magnetic field described by a Gaussian well. For this purpose, we use the quasi-one-dimensional Gross-Pitaevskii equation to describe the behavior of the condensate. In order to solve the Gross-Pitaevskii equation, we used two different approaches: one analytical (variational method) and another numerical (split-step Crank-Nicolson method). The stability of the solutions and the validation of the numerical results were confirmed, respectively, through the anti-VK criterion and the virial theorem. Furthermore, the simulations described the behavior of physical quantities of interest such as chemical potential, energy per magnon and central density as a function of the nonlinearity of the model (magnon-magnon interactions). The theoretical results provide subsidies for a better understanding of the nonlinear phenomena related to the Bose-Einstein condensates of magnons in ferromagnetic films.

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In power electronics, magnetic components are fundamental, and, unfortunately, represent one of the greatest challenges for designers because they are some of the components that lead the opposition to miniaturization and the main source of losses (both electrical and thermal). The use of ferromagnetic materials as substitutes for ferrite, in the core of magnetic components, has been proposed as a solution to this problem, and with them, a new perspective and methodology in the calculation of power losses open the way to new design proposals and challenges to overcome. Achieving a core losses model that combines all the parameters (electric, magnetic, thermal) needed in power electronic applications is a challenge. The main objective of this work is to position the reader in state-of-the-art for core losses models. This last provides, in one source, tools and techniques to develop magnetic solutions towards miniaturization applications. Details about new proposals, materials used, design steps, software tools, and miniaturization examples are provided.

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Magnetic materials have been applied in a large variety of technologies, from data storage to quantum devices. The development of two-dimensional (2D) materials has opened new arenas for magnetic compounds, even when classical theories discourage their examination. Here we propose a machine-learning-based strategy to predict and understand magnetic ordering in 2D materials. This strategy couples the prediction of the existence of magnetism in 2D materials using a random forest and the Shapley additive explanations method with material maps defined by atomic features predicting the magnetic ordering (ferromagnetic or antiferromagnetic). While the random forest model predicts magnetism with an accuracy of 86%, the material maps obtained by the sure independence screening and sparsifying method have an accuracy of ∼90% in predicting the magnetic ordering. Our model indicates that 3d transition metals, halides, and structural clusters with regular transition-metal sublattices have a positive contribution in the total weight deciding the existence of magnetism in 2D compounds. This behavior is associated with the competition between crystal field and exchange splitting. The machine learning model also indicates that the atomic spin orbit coupling (SOC) is a determinant feature for the identification of the patterns separating ferro- from antiferromagnetic order. The proposed strategy is used to identify novel 2D magnetic compounds that, together with the fundamental trends in the chemical and structural space, pave novel routes for experimental exploration.

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We present a theoretical study for the surface and bulk magnon-polaritons in magnonic crystals (or semi-infinite layered superlattices), which are formed from an array of ferromagnetic materials and nonmagnetic spacers with graphene sheets interposed between them. The external medium is taken to be vacuum. The Fermi energies in the graphene can be varied by employing different electronic doping levels, resulting in a strong influence exerted by the presence of graphene on the surface magnon-polariton modes. These effects include localization of the modes and control of the group velocities of the modes as the Fermi energies of the graphene sheets are varied, along with an important role for the phenomenological damping in the graphene sheets.

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A dinuclear copper(II) complex of formula [{Cu(bipy)(bzt)(OH2)}2(µ-ox)] (1) (where bipy = 2,2'-bipyridine, bzt = benzoate and ox = oxalate) was synthesised and characterised by diffractometric (powder and single-crystal XRD) and thermogravimetric (TG/DTG) analyses, spectroscopic techniques (IR, Raman, electron paramagnetic resonance spectroscopy (EPR) and electronic spectroscopy), magnetic measurements and density functional theory (DFT) calculations. The analysis of the crystal structure revealed that the oxalate ligand is in bis(bidentate) coordination mode between two copper(II) centres. The other four positions of the coordination environment of the copper(II) ion are occupied by one water molecule, a bidentate bipy and a monodentate bzt ligand. An inversion centre located on the ox ligand generates the other half of the dinuclear complex. Intermolecular hydrogen bonds and π-π interactions are responsible for the organisation of the molecules in the solid state. Molar magnetic susceptibility and field dependence magnetisation studies evidenced a weak intramolecular-ferromagnetic interaction (J = +2.9 cm-1) between the metal ions. The sign and magnitude of the calculated J value by density functional theory (DFT) are in agreement with the experimental data.

Assuntos

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TiO2:Co thin films on ITO (Indium-tin-oxide)/PET (Poly Ethylene Terephthalate) flexible and glass substrates were fabricated via DC magnetron co-sputtering at room temperature. The samples deposited on glass substrates were subjected to annealing processes at 473 K for 2 h to improve the crystallization of the material. Both TiO2:Co/ITO/PET and TiO2:Co/glass thin films exhibited excellent optical properties with more than 80% transmission in the visible region. An increase on ITO/PET surface temperature was detected during the synthesis of the samples; this variation in the ITO substrate ( ∼ 2 K) was associated to impact energetic of ion or atoms bombarded during the deposition process. X-ray diffraction measurements evidenced local phases to growth on the flexible substrate; the random distributions of Cobalt crystals into the rutile and anatase phases were associated to a crystalline lattice embedded with magnetic ions. A configuration of small grains and absence of cluster formation on the surface of thin films was observed through SEM and AFM measurements. From this topographic study and MFM measurements evidenced that surface grains were not constituted magnetic domains formation in the thin films. The ferromagnetic-like behavior was observed in a magnetization as function of field measurement by PPMS. M vs H curves at room temperature for TiO2:Co/ITO/PET thin films, showed the hysteresis loop. The dipolar interaction between Cobalt ions without formation of domains were correlated to the magnetic behavior in the material, as the doping concentration is lower than 12%.

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In this paper, a magnetic microwire-based sensor array embedded under the pavement is proposed as a weighing system at customs ports of entry. This sensor is made of a cementitious material suitable for embedding within the core of concrete structures prior to curing. The objective of this research is to verify the feasibility of stress monitoring for concrete materials using an array of cement-based stress/strain sensors that have been developed using the magnetic sensing property of an embedded microwire in a cement-based composite. Test results for microwire-based sensors and gauge sensors are compared. The strain sensitivity and their linearity are investigated through experimental testing under compressive loadings. Sensors made of these materials can be designed to satisfy specific needs and reduce costs in the production of sensor aggregates with improved coupling performance, thus avoiding any disturbance to the stress state.

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Tthe present work studied the cationic substitution of Y3+ by Bi3+ on the crystal structure of orthorhombic YFeO3 and its effect over magnetic, dielectric and electric properties of multiferroic yttrium orthoferrite. Stoichiometric mixtures of Y2O3, Fe2O3 and Bi2O3 were mixed and milled for 5 h using a ball to powder weight ratio of 10:1 by high-energy ball milling. The obtained powders were pressed at 1500 MPa and sintered at 700 °C for 2 h. The test samples were characterized at room temperature by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and impedance spectroscopy (IS). The X-ray diffraction patterns disclosed a maximum solubility of 30 % mol. of Bi3+ into the orthorhombic YFeO3. For higher concentrations, a transformation from orthorhombic to garnet structure was produced, obtaining partially Y3Fe5O12 phase. The substitution of Bi3+ in Y3+ sites promoted a distortion into the orthorhombic structure and modified Fe-O-Fe angles and octahedral tilt. In addition, it promoted a ferromagnetic (FM) order, which was attributed to both the crystal distortion and Dzyaloshinskii-Moriya interaction. For doped samples, an increase in real permittivity values was observed, and reduced with the increase of frequency. This in good agreement with the Maxwell-Wagner effect.

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How geomagnetic field information is collected and processed by insects for orientation and navigation remains elusive. In social insects, magnetic particles are well accepted as magnetic sensors. Ants have the ability to home and hunt, and some migratory and nomadic species can migrate or move over long distances for which magnetoreception is an important mechanism. It was shown previously that ferromagnetic resonance (FMR) spectral parameters of one migratory and one nomadic ant could be distinguished from Brazilian Solenopsis ant species and that these parameters correlate to the local geomagnetic field. The present work focuses on genera engaged in long-distance group raids and emigration collected mainly in the Amazon rainforest. A diversity of specimens of the genus was individually measured by FMR. Cluster analysis of the occurrence of the FMR Low Field component, associated with large or aggregated nanoparticles, and their spectral angular dependence resulted in a phylogenetic dendrogram of the genera of ants, principally from the North Brazilian region. The magnetic material characteristics of ants of the Invertebrate Collection from the Museum Paraense Emilio Goeldi were tested looking for their relation to ant genera and the local geomagnetic field. The observed spectral differences of the magnetic particles suggest that they are related to their capacity for adaptation to their environment and/or to displacement behaviour.

Assuntos

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Ferritin has been studied in many animals, plants and bacteria. The main functions of ferritin in mammals are iron concentration and stabilization, protection against oxidants and iron storage for later developmental or iron-dependent activities. Although insect ferritin plays a key role in iron transport, only a few studies to date have examined its properties and function. Ferritin isolation from the haemolymph of adult Camponotus sericeiventris ants involved heating at 75 °C, followed by protein fractionation with 3.2 M KBr gradients and ferritin sedimentation with KBr. Protein identification was performed using high-resolution proteomics techniques. SDS-PAGE revealed three subunits with molecular weights (MW) of 26, 28 and 31 kDa. Native PAGE indicated a MW higher than 669 kDa. Proteomic analysis strongly suggested the 26 and 31 kDa bands as F2LCH and F1HCH subunits of ferritin, respectively. Ferromagnetic resonance (FMR) at 100 K showed, at low field, a characteristic broad component of the ferritin iron core, suggesting that its distribution was shifted to values greater than 3000, a higher content than in mammals. The protein yield and MW were comparable to those reported in other studies of insects. To the best of our knowledge, this is the first report on ferritin extracted from adult ants to date. These results are discussed on the basis of the protein structure-function relation of secreted insect and mammal ferritins. This purification method will allow the use of magnetic techniques, which are relevant for understanding the role of ferritin in the biomineralization of magnetic nanoparticles in insects.

Assuntos

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Implicit constitutive relations that characterize the response of elastic bodies have greatly enhanced the arsenal available at the disposal of the analyst working in the field of elasticity. This class of models were recently extended to describe electroelastic bodies by the present authors. In this paper, we extend the development of implicit constitutive relations to describe the behaviour of elastic bodies that respond to magnetic stimuli. The models that are developed provide a rational way to describe phenomena that have hitherto not been adequately described by the classical models that are in place. After developing implicit constitutive relations for magnetoelastic bodies undergoing large deformations, we consider the linearization of the models within the context of small displacement gradients. We then use the linearized model to describe experimentally observed phenomena which the classical linearized magnetoelastic models are incapable of doing. We also solve several boundary value problems within the context of the models that are developed: extension and shear of a slab, and radial inflation and extension of a cylinder.

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The presence of magnetic material in tissues of lateral line and ocellar spot of tomtates Haemulon aurolineatum is shown using the ferromagnetic resonance technique. For the first time magnetic material is reported in the ocellar spot. The magnetic material detected in these structures of H. aurolineatum suggests that this species could use magnetic orientation during its nocturnal foraging, and the relevance and role of this material with respect to schooling movements is discussed.

Assuntos