Magnetic Properties Of Materials Research Articles

In unison magnetization reversal in a magnetoelastic bilayer structure

Due to the magnetostriction effect, a magnetic material changes its dimensions when it is magnetized. In this work, we show how in a magnetostrictive bilayer structure comprising two materials with magnetostriction constants of opposite signs, the magnetic switching is affected by magnetoelastic coupling. While the layer with positive magnetostriction tries to elongate in the direction of the applied magnetic field, the layer with negative magnetostriction tries to contract. In the studied bilayers, the mechanical influence of each magnetostrictive layer on the other is of the opposite sign because of their opposite magnetostrictive constants. Since magnetoelasticity is not an interfacial interaction but an intrinsic property of magnetic materials, the mechanical strain promoted by the applied magnetic field affects the layers as a whole. The net effect is a simultaneous reversal of magnetization of the two layers regardless of their thicknesses. This behavior has been studied in bilayers with different thickness ratios comprising Ni90Fe10, negative magnetostriction and Fe70Ga30, positive magnetostriction. These results demonstrate the possibility of using this physical mechanism to beat the critical limit thickness imposed by interfacial interactions in magnetically coupled multilayers in such a way that the magnetization reversal is made in unison regardless of the layer thickness.

Heterostructured C@Fe3O4@FeSiCr composite absorbing material derived from MIL-88(Fe)@FeSiCr

The C@Fe3O4@FeSiCr composites with carbon-covered heterostructures were obtained by constructing C and Fe3O4 derived from carbonized MIL-88(Fe)@FeSiCr to form heterogeneous interfaces with FeSiCr. The electromagnetic parameters of the composites were regulated by adjusting the compound amount of MIL-88(Fe). The impedance matching performance was optimized, and this further improved the microwave absorbing performance. At a MIL-88(Fe) compound amount of 30 wt%, the composite achieves a minimum reflection loss (RLmin) of –68.07 dB at 4.83 GHz with an absorbing coating thickness of 3.33 mm. In the field of microwave absorbing materials, these results provide valuable guidelines for constructing heterogeneous interface coatings and optimizing the impedance matching properties of soft magnetic alloys materials.

EPR Spectrum Analysis of DPPH and MnCl2

This paper presents the findings of electron paramagnetic resonance (EPR) spectroscopy experiments conducted on two different samples: 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Manganese Chloride (MnCl2) dissolved in H2O. The experiments were conducted at Dr. D. Petasis EPR lab located in Allegheny College, Meadville, PA, USA. A Varian X-Band spectrometer was utilized for the analysis of the EPR absorption spectra. The primary objective was to determine the g-values and hyperfine structure of the two samples, which can be crucial in characterizing their electronic properties. The g-values obtained for both DPPH and MnCl2 were found to be remarkably close to the theoretically calculated values, suggesting the high accuracy and success of the experiments. This agreement validates the reliability of the EPR measurements and demonstrates the precision of the instruments and experimental procedures employed. For the MnCl2 sample, a hyperfine structure with 6 visible EPR lines was observed. By analyzing the number of EPR lines, the nuclear spin of the Mn(II) ion was determined to be I = 5/2, consistent with the expected value for Mn(II). The hyperfine constant (A) was also calculated from the field position differences between adjacent lines, providing further insights into the sample's magnetic properties. Comparisons were made between the obtained g-values and hyperfine constant with the expected values for Mn(II) in the literature, confirming the accuracy of the measurements and reinforcing the credibility of the experimental data. Overall, the EPR spectroscopy experiments conducted on DPPH and MnCl2 in H2O have provided valuable information about the electronic and magnetic properties of these paramagnetic materials. The results demonstrate the effectiveness of EPR spectroscopy as a powerful experimental technique for investigating various bio-chemical samples and understanding the effects of solvents on the EPR spectra of compounds. The close agreement between the experimental and theoretical values for the g-factors and hyperfine constants reinforces the reliability of the data obtained from the EPR experiments.

Properties of “Higher Manganese Silicide-Silicon” Heterostructure

Based on the diffusion technology, many scientists and specialists have conducted research on obtaining materials that are fundamentally different in electrical and photo-thermal parameters from the original material by introducing various input atoms into semiconductor materials and creating deep energy levels in their band gap. The electrical, photoelectric, optical, and magnetic properties of these semiconductor materials have been extensively studied with metal group elements, isovalent elements, and rare earth elements added to silicon through the process of growth, ion implantation, or diffusion from the gaseous state. The technology of introducing impurity atoms into silicon by the diffusion method is distinguished from other methods in its simplicity, energy efficiency, and low cost. Up-to-date, the technology of changing the resistivity and conductivity of the initial sample by diffusion of manganese atoms into single-crystal silicon is studied insufficiently. In the article, it was determined that when manganese atoms diffuse into silicon, a high-manganese silicide is formed on its surface and in the near-surface layer. Based on the analysis of the experimental results, the thermal EMF (electromotive force) in Mn4Si7-Si -<Mn>-Mn4Si7 structures in a certain temperature range and under illumination (with monochromatic or integrated light) is explained by the fact that it based on the Pelte effect, observed in semiconductors.The volt-ampere characteristics (VAC) of the obtained structures were measured at various temperatures, in the dark and in the light. Formation of a boundary layer with high resistivity at the boundary of the higher manganese-silicon transition, the transition from higher manganese silicide to the base of the structure due to the effect of ionization of pores during illumination of structures and external influence. The applied field was clarified based on VAC results. The manganese high silicide layer formed on the silicon surface has the properties of a semiconductor, and the formation of a heterojunction upon transition to silicon is shown on the basis of the sphere diagram.

Modulating above-room-temperature magnetism in Ga-implanted Fe5GeTe2 van der Waals magnets

The creation of van der Waals (vdW) ferromagnets with tunable Curie temperature (TC) and magnetic anisotropy is essential in developing vdW magnet-based devices. Here, we report an effective and reliable method for modulating the magnetic properties of vdW Fe5GeTe2 by site-specific Ga+ implantation. In this study, we report an easy axis in the ab-plane for bulk Fe5GeTe2 (TC = 310 K) and an axis out of the plane for thin Fe5GeTe2 flakes (TC = 290 K). Combining element-resolved photoemission electron microscopy and spatially resolved magneto-optic Kerr microscopy, we find that the implantation of a tiny amount of 10−3 Ga+·Å−3 in Fe5GeTe2 greatly enhances the TC from 290 to 360 K and switches the magnetic easy axis from the out-of-plane c axis to the ab-plane. The room-temperature x-ray magnetic circular dichroism signal is enhanced from 0% to 9% at an implantation level of 10−2 Ga+·Å−3. These results provide new opportunities for tailoring the magnetic properties of vdW materials beyond room temperature.

Is a 2D Nanostructured Surface Capable of Changing the Corrosion and Magnetic Properties of an Amorphous Alloy?

In this work, an attempt was made to reveal and explain the influence of the process of formation of 2D nanostructures at the surface of an amorphous alloy (an alloy with the composition Co75Si15Fe5Cr4.5Al0.5 (in at.%) was used for this purpose) on the corrosion and magnetic properties of such an alloy. Two-dimensional nanostructures (nanocells of 100-150 nm in size, which were obtained by anodizing the initial sample in an ionic liquid) are essentially a pattern on the surface of the sample, and they cannot completely cover and block the surface from external effects. It was postulated that the presence of these nanostructures during corrosion and magnetic tests has no significant effect. However, a noticeable inhibition effect was observed during corrosion tests and a less noticeable (but still detectable) effect was observed during magnetic tests. The authors believe that the effect obtained, with a detailed study, can be used to increase the corrosion resistance and to improve the properties of traditional magnetic materials.

Structural, Electronic & Magnetic Properties of Pristine and Defected ZnO Monolayer: First-Principles Study

Electronic and magnetic properties of materials are appealing properties and have budding applications in the devices. In this work, we have investigated the structural, electronic and magnetic properties of pristine Zinc-Oxide (ZnO) and Oxygen-defected Zinc-Oxide (ZnO_O) materials by spin-polarized density functional theory (DFT) method. Structural properties are studied by calculating their total ground state energy, and found that both are stable 2D materials. It is also found that ZnO have higher stability than of ZnO_O material. Electronic properties of considered materials are examined by analyzing of their band structure, density of states (DOS) calculations and found that ZnO is a direct band gap, n-type semiconductor material in its pristine form and an indirect band gap, p-type semiconductor material in its Oxygen-defected form (ZnO_O). Magnetic properties of pristine and defected ZnO are investigated by analyzing their density of states (DOS) and partial density of states (PDOS) calculations, they revealed that ZnO and ZnO_O have non-magnetic properties.

Heterostructured Cobalt Silicide Nanocrystals: Synthesis in Molten Salts, Ferromagnetism, and Electrocatalysis.

Nanoscale heterostructures of covalent intermetallics should give birth to a wide range of interface-driven physical and chemical properties. Such a level of design however remains unattainable for most of these compounds, due to the difficulty to reach a crystalline order of covalent bonds at the moderate temperatures required for colloidal chemistry. Herein, we design heterostructured cobalt silicide nanoparticles to trigger magnetic and catalytic properties in silicon-based materials. Our strategy consists in controlling the diffusion of cobalt atoms into silicon nanoparticles, by reacting these particles in molten salts. By adjusting the temperature, we tune the conversion of the initial silicon particles toward homogeneous CoSi nanoparticles and core-shell nanoparticles made of a CoSi shell and a silicon-rich core. The increased interface-to-volume ratio of the CoSi component in the core-shell particles yields distinct properties compared to the bulk and homogeneous nanoparticles. First, the core-shell particles exhibit increased ferromagnetism, despite the bulk diamagnetic properties of cobalt monosilicide. Second, the core-shell nanoparticles act as efficient precatalysts for alkaline water oxidation, where the nanostructure is converted in situ into a layered cobalt silicon oxide/(oxy)hydroxide with high and stable oxygen evolution reaction (OER) electrocatalytic activity. This work demonstrates a route to design heterostructured nanocrystals of covalent intermetallic compounds and shows that these new structures exhibit very rich, yet poorly explored, interface-based physical properties and reactivity.

Magnetoelectric properties of multiferroic ceramic composites

The paper analyzes the influence of hard and soft admixture on the functional properties of multiferroic ceramic composites. Two composite materials via solid-state reaction route were obtained. PZT-type materials (with hard or soft admixture) were selected as the ferroelectric component (90%), and nickel–zinc ferrite as the magnetic component (10%). The influence of the doping type (soft and hard admixture of the ferroelectric composite component) on multiferroic composites’ dielectric, ferroelectric, electromechanical, magnetic, and magnetoelectric properties were analyzed. Microstructural studies revealed the microstructure of composites with the correct distribution of the magnetic component in the ferroelectric matrix, suitable for maintaining both the ferroelectric and magnetic properties of composite materials. Research has shown that using a ferroelectric component as the PZT (from the morphotropic region and doped with the ferroelectrically soft niobium admixture) shows many advantages, positively influencing the functional properties of the multiferroic composite. It ensures effective polarization of the composite sample, obtaining a high magnetoelectric effect, which is required in sensors or magnetoelectric converters. PZT with a hard admixture shows higher stability of physical parameters, but its characteristic property also hinders the effective polarization of the composite sample.

Symmetry-dependent magnetic, electric and optical properties in ferroic and multiferroic materials

Symmetry-dependent magnetic, electric and optical properties in ferroic and multiferroic materials

Microstructure, mechanical and soft magnetic properties of in-situ TiC reinforced Fe27.5Ni27.5Co45-based medium entropy composites

The insufficient mechanical properties of conventional soft magnetic materials (SMMs) hinder their widespread applications, and unfortunately, traditional strengthening mechanisms could dramatically deteriorate their soft magnetic properties without adjusting the alloy composition. Here, we developed TiC/Fe27.5Ni27.5Co45 medium-entropy composites (MECs) possessing multi-scale microstructure consisting of ultrafine and micron-sized grains by introducing in-situ formed TiC nano particles during the spark plasma sintering (SPS) process. Compared with the precipitate-free Fe27.5Ni27.5Co45 medium-entropy alloy, TiC/Fe27.5Ni27.5Co45 MEC with ∼ 8.7 vol% TiC (noted as Ti5-MEC) demonstrated a significant improvement in compressive yield strength (from 459 MPa to 1114 MPa), attributing to the grain-boundary strengthening and dispersive precipitation strengthening, as well as hetero-deformation induced (HDI) strengthening. Meanwhile, the Ti5-MEC exhibits a high saturation magnetization (Ms) of 153.1 emu/g and a low coercivity (Hc) of ∼ 8.2 Oe, indicating excellent soft magnetic properties, primarily due to the multi-scale microstructure. Our work has demonstrated that engineering multi-scale microstructures in MECs is an effective strategy to achieve desirable combinations of soft magnetic and mechanical properties.

Role of 5 mol% rare earth (La3+) on the structural, microstructural, and magnetic properties of cobalt chromite ceramics

Spinel oxides, which have the structure AB2O4 and are distinguished by their exceptional magnetic, electric, and multiferroic properties and exhibit a wide range of functional responses in the category of oxides. The cobalt chromate (CoCr2O4) is well-known as a multiferroic-magnetoelctric (ME) material. It belongs to the magnetic spinal oxide family and is noted for its complicated spiral ferromagnetic(FM) orderings. To enhance the magnetic properties of the CoCr2O4, in this work we have chosen Lanthanum (La3+) 0.05 mol% doped cobalt chromites (CoCr2O4) nanoparticles. The solution combustion method was utilized to synthesize the nanomaterial, where urea and glucose were used as fuels. The Structural exploration of the Co0.95La0.05 Cr2O4 nanoparticles were clarified using powder X-ray diffraction. To understand the microstructure properties we have carried out high-resolution electron microscopy and it reveals highly porous nature. In FTIR spectra the two main absorption bands at 507 cm−1 and 616 cm−1 were observed which confirm the formation of spinal chromates. The TGA results revealed a slow thermal degradation, and the sample has a thermal stability that is greater than the temperature range tested. Researchers have examined the changes in temperature and magnetic field affected the magnetic properties of materials over time (ZFC & FC). In comparison to the bulk sample, the Curie temperature at which samples transition from a paramagnetic (PM) state to a collinear short-range ferromagnetic (FM) state is significantly lower. This temperature is denoted as TC-98 K deteriorated with time in terms of quality. At low temperatures, there is no magnetic transition that can be identified between the short-range FM order and the long-range spiral spin structure. This is in contrast to the magnetic transitions that can be discovered in bulk. What gives rise to all of the intriguing qualities that have been described above is the presence of weak magnetic frustration, which is very much connected to super-exchange interactions and is found along different paths such as A-O-A, B–O–B, and A-O-B. This presence is what gives rise to all of the intriguing characteristics that have been described above.

Tuning the magnetic and magnetocaloric properties of a compound via mixing (1–x).La0.67Ca0.33MnO3 +x.La0.67Sr0.33MnO3 (x = 0, 0.25, 0.50, 0.75, 1): Composite materials or composite compounds?

This study aims to optimize the magnetic and magnetocaloric properties of composite materials (or compounds) produced by mixing different ratios of two manganite compounds having different structural, magnetic, and magnetocaloric properties. The parent compounds were prepared using the sol–gel production method and the ultrasonic bath mixing technique was involved to prepare desired composite materials. SEM analyses revealed that the parents and composite materials have the same surface morphologies except for their grain sizes. EDS analyses were performed to identify the possible/candidate phases in the composite materials. These candidate phases are involved in refining XRD data. The fact that the Curie temperatures (TC) of the composite materials were found to be much higher than those of the parent compounds was another proof that composite compounds were obtained instead of composite materials by using the ultrasonic bath mixing technique. Although the TC of the composite compounds was higher than those of the parent compounds, the maximum magnetic entropy values were found to vary between the maximum magnetic entropy valuesof the parent compounds.

Latest Developments in the Hardspot Inspection of heavy plates

Hard Spots are local areas with increased hardness on the surface of semi-finished or end products in steel manufacturing. The cause of these hard spots is attributed to effects in the casting or rolling process. In general, the occurrence of hard spots cannot be avoided completely in production of heavy plates. Therefore, in various current line-pipe specifications the topic ‘hard spots’ is discussed and there is actually a strong request for a suitable test method from end users as well as manufacturers of line pipes. The current presentation should give an update on the ongoing developments. Basis of all current approaches are electromagnetic inspection methods, based on the correspondence in between electrical and magnetic material properties and physical hardness. To be able to integrate an inspection into the production process, the so called rolling skin or mill scale, a thin surface layer of different iron oxides with different material properties to the base material, should not influence the inspection results. The inhomogeneities of this rolling skin, especially in conductivity and permeability, normally render standard eddy current inspection impossible. Additionally in the standard production process, the products were handled by large cranes, manipulating the plates by strong magnets. These magnets leave behind a significant residual magnetization. To overcome both problems the method uses a strong alternating magnetization to measure different resulting micro magnetic parameters. By combining these parameters, the mill scale as well as the residual magnetization effects can be minimized, so it gets possible to measure small local hardness variations on the plates. The presented paper describes the actual progress of the inspection method itself including the theoretical background as well as the calibration on artificial hard spots. Furthermore, an outlook will be given to the implementation in an automatic inline inspection system for plate mills.

Effect of sintering temperature on structural, electrical, and magnetic properties of Bi2Fe4O9 polycrystalline materials

In the present paper, the effect of sintering temperatures (500 0C to 800 0C) on structural, and multiferroic properties of double perovskite Bismuth Ferrite (Bi2Fe4O9) materials synthesized through co-precipitation method has been investigated. The Powder X-ray diffraction and Raman spectroscopic studies revealed the formation of Mullite type Bismuth Ferrite (Bi2Fe4O9) with orthorhombic (Pbam) structure. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) investigations reveal the formation of cuboid shape nanoparticles closely packed to each other. The particle size increases with increasing the sintering temperature from 500 0C to 800 0C. The Transmission electron microscopic (TEM) technique employed in both imaging and diffraction modes also confirms the growth of cubic nanocrystals of Bismuth Ferrite (Bi2Fe4O9). The saturated polarization–field curves for all samples sintered at different temperatures indicate the improvement of ferroelectric properties. The magnetic properties of Bi2Fe4O9 were investigated through hysteresis loops. The unsaturated curve of the magnetic field-dependent magnetization (M−H) of the materials at room temperature exhibits anti-ferromagnetic behavior.

Speed control of switched reluctance motors based on fuzzy logic controller and MATLAB/Simulink

Switched reluctance motors (SRM) becomes increasingly popular due to its simple structure and dependability. It seems to have a two-pole configuration. A stator had also centralized coils along each pole, whereas a rotor has an iron core only. As a result, the switched reluctance motor is anticipated to be a low cost, incredibly robust variable-speed machine. Because the switched reluctance motor is only made up of laminated coils, its performance is heavily reliant on the magnetic properties of the core material. Vibration, torque ripple, and low torque for each unit volume are some of their drawbacks. Typically, a standard proportional-integral-derivative (PID) controller is designed to regulate the Switched Reluctance Motor's speed. Furthermore, the PID controller could also regulate and control SRM when the load changes abruptly. A fuzzy logic controller (FLC) is utilized within this article to regulate the speed of the SRM drive. The MATLAB/Simulink platform is used to analyze the behavior of SRM with FLC. To demonstrate FLC's superiority, its results have been compared to that of a typical PID controller.

Ultra-Miniature and Circularly Polarized Ferrite Patch Antenna

This paper describes the development, the design and the measurement of a circularly polarized ultra-miniature antenna. The modelled device takes advantage of the magnetic properties of ferrite materials to achieve the desired specifications. Indeed, the antenna is operating at a frequency where the effective permeability is greater than 1 and the permeability has a negative real part, i.e. in the zone between the μ and μ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</i> resonances of the ferrite. The dimensions of the designed antenna are about λ0/23.6×λ0/20.7×λ0/29.4 at 2.42GHz and a good circular polarization is achieved at the central operating frequency of the device, with a boresight axial ratio of 1.6dB. This paper is based on the modal study of a ferrite cavity which will be presented and detailed in a first step. The physical properties of the antenna and related material (dimensions, ferrite internal magnetic field, the saturation magnetization, etc.) will be deduced from this modal study and from the resolution of the wave equation inside a cylindrical ferrite cavity. All the antenna performances in terms of impedance matching, axial-ratio and radiation pattern are reported and commented. This concept is finally validated by the measurement of a prototype.

The coupling between the interlayer magnetic order and Davydov splitting modes in few-layer CrI3

The magnetic order in 2D material CrI3 has a significant impact on the Raman polarization selection rules of phonons, as evidenced by magneto-optical Raman spectroscopy. In a monolayer, the forbidden Raman scattering of A1g mode can be detected in the XY channel at low temperatures. However, in the bilayer, the Ag mode splits into two modes, and the selection rules of the splitting modes are determined by the magnetic order and symmetry. In contrast, the inversion symmetry of the spin structure is maintained in both antiferromagnetic (AFM) and ferromagnetic (FM) states in the trilayer (3L) CrI3, and the evolution of its Raman scattering with magnetic field is not yet clear. In this work, we use magneto-optical polarized Raman spectroscopy and reflective magnetic circular dichroism to investigate the Davydov splitting of the Ag phonon mode and its coupling to layered magnetism in 2–5L CrI3. Our results show that the Raman scattering of the Ag mode is strongly coupled to the layered magnetic order, indicating strong spin–phonon coupling in CrI3. Our study might shed light on the research on interaction between magnetic and vibrational properties of 2D magnetic materials and provide important implications for developing novel 2D spintronic devices.

Experimental and theoretical assessment of the Eu3+ doped Bi4Ge3O12

In this work, Bi4Ge3O12 doped with Eu3+ was investigated experimentally and theoretically. The synthesis of several samples with different Eu3+ concentrations was carried out by the polymeric precursor method. Photoluminescence spectroscopy was performed, and it shows the typical electronic transitions of Eu3+. FTIR interpretation of samples allows us to infer that Eu3+ substitutes not only Bi3+ but also Ge4+. This interpretation was corroborated by ab initio calculations as both substitutions were found to be thermodynamically stable. Eu3+ naturally takes on the Bi3+ sites, producing ferromagnetic alignment; but when Eu3+ takes on the Ge4+ sites the alignment becomes antiferromagnetic. Since rare earth elements are particularly important in modifying the magnetic and luminescent properties of host materials, our findings open a new way to give a bi-functionality to the Bi4Ge3O12 material through selective doping.

Effect of Chromium Substitution on Microstructure and Magnetic Properties of La&lt;sub&gt;0.7&lt;/sub&gt;Sr&lt;sub&gt;0.2&lt;/sub&gt;Ba&lt;sub&gt;0.1&lt;/sub&gt;Mn&lt;sub&gt;1-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Cr&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;x&lt;/i&gt; = 0, 0.03, 0.05, 0.07, 0.1)

Structure, morphology, and magnetic properties of perovskite La0.7Sr0.2Ba0.1Mn1-xCrxO3 (x = 0; 0.03; 0.05; 0.07 and 0.1) synthesized via sol-gel method have been studied. X-ray diffraction studies confirm the Rhombohedral structure with R-3c space groups for all samples. The magnetization measurements clearly show that magnetization decreases with increasing Cr substitution concentration. The partial substitution of Cr3+ in the Mn site weakens the ferromagnetic double exchange interaction of the Mn3+–O–Mn4+ bond. It is caused by the emergence of the Cr3+–O–Cr3+ antiferromagnetic interaction. As known, the structural parameters affect the magnetic properties of perovskite manganese materials in the double exchange interaction. As the Cr3+ concentration increases, the average Mn-O bond length also increases, and the average Mn-O-Mn bond angle decreases, which dramatically weakens the Mn3+–O–Mn4+ double exchange interaction.