Magnetic Transformation Research Articles

Substitution-driven structural, optical and magnetic transformation of Mn, Co co-doped BiFeO3

Substitution-driven structural, optical and magnetic transformation of Mn, Co co-doped BiFeO3

Theoretical Study on BiCoO3: Pressure‐Tuned Transformation of Structure, Magnetism, Charge, and Spin State

AbstractThe atomic structures, electronic structures, magnetic properties, and spin states of BiCoO3 multiferroic material under hydrostatic pressure are comprehensively investigated by using first‐principles calculation based on density functional theory. Firstly, we found the pressure‐tuned structural symmetry transition from tetragonal P4 mm (No. 99) to cubic Pmm (No. 221) space group. The structural transformation prompts the Co─O polyhedral coordination transfer from a CoO5 pyramidal to a CoO6 distorted octahedron. Secondly, the pressure‐induced magnetic change from C‐type antiferromagnetic state to ferromagnetic state and then to paramagnetic configuration occurred after continuous compression of the volume. Essentially, the fundamental reason for the transition of the magnetic structure lies in the change of the internal atomic structure, such as the pressure induced abrupt changes of Co─O bond length and <Co─O─Co> bond angle. Meanwhile, an obvious volume collapse was observed when the pressure was applied to 51–56 GPa. Finally, as the pressure increases, the magnetism changes from C‐type antiferromagnetic state to paramagnetic configuration, accompanying the transformation from high spin state with b2g2eg2a1g1b1g1 configuration in pyramid structure to low spin state with t2g6eg0 in octahedral field. Therefore, our results demonstrate that applied hydrostatic pressure in BiCoO3 can trigger the transformation of structure, magnetism, charge, and spin state.

Calorimetric Studies of Phase Transformations in the La<sub>1 – x</sub>Y<sub>x</sub>Mn<sub>2</sub>Si<sub>2</sub> System

Differential scanning calorimetry (DSC) is used to determine the magnetic phase transformation temperatures of the La1 – xYxMn2Si2 (x = 0–1) alloys. For the compositions with х from 0 to 0.3, the temperature dependences of DSC signal exhibit λ-like endothermic effects observed near 300 K, which are related to the magnetic phase transition from the ferromagnetic to layered antiferromagnetic structure, and weak anomalies, which are observed in a temperature range of from 458 K for the composition with х = 0 to 323 К for the composition with х = 0.3 upon disordering of the layered antiferromagnetic structure. A clear endothermic peak corresponding to the disordering of interplane antiferromagnetic layered structure was found for the YMn2Si2. The data obtained are used to construct the magnetic phase diagram of the La1–xYxMn2Si2 system in a temperature range of 270–600 К. The differential scanning calorimetry is shown can be successfully used for the determination of temperatures of various magnetic phase transformations in rare-earth intermetallic compounds.

Evaluation of DSRD-based pulsers for a Dielectric Wall Accelerator

Silicon (Si) drift step recovery diodes (DSRD) are opening switches that form the basis for nanosecond-scale high voltage (HV) pulsers. These pulsers are crucial to the operation of a dielectric wall accelerator (DWA), a compact particle accelerator design for proton beam radiation therapy. For the DWA to operate properly, the pulser must generate HV pulses with fast rise times and widths on the order of 1 ns at an operating frequency above 1 kHz. Several pulser designs are available that can optimally drive DSRDs. The purpose of this study is to investigate the capabilities of two DSRD-based pulsers in the context of the DWA and the required pulse parameters. The first pulser is based on a magnetic saturation transformer (MST) and a DRSD. The second pulser considered is a multi-module MOSFET-DSRD-based pulser. Additionally, Sentaurus TCAD simulations are used to study the influence of the Si DSRD doping profile on the output pulse shape. The MST-DSRD-based pulser is able to generate higher amplitude pulses than the MOSFET-DSRD-based pulser with a single module (9645 V and 1807 V, respectively). However, the multi-module MOSFET-DSRD-based pulser achieves the maximum pulse amplitude (10.9 kV) compared to MST-DSRD-based pulser (9645 V). The MOSFET-DSRD-based pulser also generates pulses with shorter pulse widths compared to the MST-DSRD-based pulser (minimum of 3 ns vs. minimum of 8.36 ns, respectively). With no compression stage, the MOSFET-DSRD-based pulser (with more than one module) generates pulses with consistently faster rise times (≤3.06 ns) compared to the MST-DSRD-based pulser (≤4.31 ns). With a compression stage, the rise times were comparable between the two pulsers (MOSFET-DSRD: 1.66 ns and MST-DSRD: 1.48 ns). Both pulsers are able to operate at 1 kHz and the MOSFET-DSRD-based pulser up to 10 kHz. Parasitic capacitance and coupling between modules of the MOSFET-DSRD-based pulser affect the pulse through their influence on the forward and reverse pumping duration. Simulations show that the p region of the DSRD should be larger than the n doped region. Simulations including a parasitic capacitance, modelling the electrical connections to the DSRD, reduce the pulse amplitude. Simulations of the pulsers incorporating SiC DSRDs show a reduction in the pulse amplitude and a widening of the pulse width in comparison to the Si DSRDs.

Magnetic phase transition and critical behavior of the chiral magnet [formula omitted]-Mn type Co7Zn7Mn6

We report a systematic study of magnetic transformation and magnetic critical behavior in the chiral magnet β-Mn type Co7Zn7Mn6. It undergoes a paramagnetic-ferromagnetic phase transition around 190 K and shows a spin glass state at 18 K. The critical exponents β= 0.685, γ= 1.385, and δ= 3.03 are obtained by the investigation of magnetic field dependence on magnetic-entropy change and the calculation with Widom scaling relation. The reliability of critical exponents is confirmed by the scaling equation. The strong reversed site disorder of β-Mn type Co7Zn7Mn6 results in the localized characterization of carriers and a slow development of ferromagnetic ordering state.

Magnetization and phase transformation in Fe-Ga and Fe-Ge alloys

The magnetic properties and structural states of Fe-Ga and Fe-Ge alloys, known for their large magnetostriction, have been investigated. Experimental characterizations are supported by ab initio calculations and Monte Carlo simulations to reveal the complex interplay between magnetic properties and structural changes. Our findings are in agreement with previous investigations and show that the Curie temperature (TC) of these alloys changes gradually with increasing alloying element concentration while the A2 solid solution is being realized. Further alloying of Fe-Ga leads to the transition from a single-phase to a two-phase A2 + D03 state and results in two distinct TC values. At the same time Fe-Ge shows a more complex behavior with several phase transitions influencing the magnetic ordering temperatures. Theoretical calculations suggest a significant correlation between the magnetic moments, exchange interactions, and observed TC trends. It is shown that the D03 phase is characterized by the lowest TC among other phases. Using Monte Carlo simulations, we found that in ferromagnetic state of Fe-Ge alloy the D03 ordering develops homogeneously, while in Fe-Ga it follows a nucleation and growth scenario.

Pole-Wrapped Negative Equivalent Magnetic Reluctance Structure-Based Transformer for Line-Frequency Isolation-Dependent Applications

Pole-Wrapped Negative Equivalent Magnetic Reluctance Structure-Based Transformer for Line-Frequency Isolation-Dependent Applications

Analyzing the Sequence of Phases Leading to the Formation of the Active Region 13664, with Potential Carrington-like Characteristics

Abstract Several recurrent X-class flares from Active Region (AR) 13664 triggered a severe G5-class geomagnetic storm between 2024 May 10 and 11. The morphology and compactness of this AR closely resemble the AR responsible for the famous Carrington Event of 1859. Although the induced geomagnetic currents produced a value of the Dst index, probably 1 order of magnitude weaker than that of the Carrington Event, the characteristics of AR 13664 warrant special attention. Understanding the mechanisms of magnetic field emergence and transformation in the solar atmosphere that lead to the formation of such an extensive, compact, and complex AR is crucial. Our analysis of the emerging flux and horizontal motions of the magnetic structures observed in the photosphere reveals the fundamental role of a sequence of emerging bipoles at the same latitude and longitude, followed by converging and shear motions. This temporal order of processes frequently invoked in magnetohydrodynamic models—emergence, converging motions, and shear motions—is critical for the storage of magnetic energy preceding strong solar eruptions that, under the right timing, location, and direction conditions, can trigger severe space weather events on Earth.

The second-order magnetic transformation and magnetocaloric effect in all-d-metal Heusler ribbon Ni35Co15Mn34Ti16

The new all-d-metal Heusler alloys with good mechanical properties are candidates for magnetocaloric materials compared other famous refrigeration materials. In this work, Ni35Co15Mn34Ti16 ribbon with a second-order magnetic transformation was investigated for magnetoclaoric effect. It crystalizes pure B2 structure at room temperature and undergoes a SOMT at Curie temperature in austenite (TCA = 358 K) between paramagnetic and ferromagnetic phase. A large saturation magnetization (MS) at 5 K is 166 emu/g. The maximum values of magnetic entropy change (−ΔSM) and the temperature-averaged entropy change TEC(10 K) reach 1.62(3.42) J kg−1 K−1 and 1.64 (3.44) J kg−1 K−1 with magnetic field change (ΔH) of 20(50) kOe, respectively, which are comparable to most of other all-d-metal Heusler alloys.

An integrated exploration from microstructure to mechanics in austenite to pearlite transformation of high carbon steel under high magnetic fields

The effects of a high magnetic field (12 T) on the microstructural evolution and mechanical properties of high carbon steel during isothermal pearlitic transformation at 720 °C were investigated. The application of a high magnetic field effectively promotes pearlitic transformation and leads to a reduction in the lamellar spacing and the geometrically necessary dislocation density (GND) as well as to a slight increase in the grain size of the pearlite, which leads to a decrease in hardness. This is because the magnetic field reduces the magnetic Gibbs energy of ferrite and cementite, resulting in an increase in the driving force of phase transformation, which shortens the pearlite maturation time and reduces the nucleation barriers of pearlite, thereby accelerating the growth rate of pearlite. In addition, the interfacial energy of ferrite/cementite was found to be increased by the magnetic field from the thermodynamic point of view, and the mechanism of action of the magnetic field -induced precipitation of cementite in the form of particles and short rods was elucidated. The present work will enhance the understanding of the mechanism of magnetic field-induced phase transformation in iron-based materials.

Modelling of negative equivalent magnetic reluctance structure and its application in weak-coupling wireless power transmission

In weak-coupling wireless power transmission, increasing operating frequency, and incorporating metamaterials, resonance structures or ferrite cores have been explored as effective solutions to enhance power efficiency. However, these solutions present significant challenges that need to be addressed. The increased operating frequency boosts ferrite core losses when it exceeds the working frequency range of the material. Existing metamaterial-based solutions present challenges in terms of requiring additional space for slab installation, resulting in increased overall size. In addition, limitations are faced in using Snell’s law for explaining the effects of metamaterial-based solutions outside the transmission path, where the magnetic field can not be reflected or refracted. To address these issues, in this work, the concept of a negative equivalent magnetic reluctance structure is proposed and the metamaterial theory is extended with the proposed magnetic reluctance modelling method. Especially, the negative equivalent magnetic reluctance structure is effectively employed in the weak-coupling wireless power transfer system. The proposed negative equivalent magnetic reluctance structure is verified by the stacked negative equivalent magnetic reluctance structure-based transformer experiments and two-coil mutual inductance experiments. Besides, the transmission gain, power experiments and loss analysis experiments verify the effectiveness of the proposed structure in the weak-coupling wireless power transfer system.

A new winding structure with low common‐mode current in input series output parallel planar transformer LLC converter

AbstractMHz switches and integrated magnetic planar transformers (PT) promote the high density and miniaturization of DC/DC converters. The parasitic parameters of the PT at high frequency significantly affect the performance of converters, resulting in severe electromagnetic interference (EMI) problems. Firstly, this paper proposes a new common‐mode (CM)‐suppression winding structure for the input series output parallel (ISOP) matrix transformer LLC converter. The sources and conduction principle of CM noise are analyzed. Furthermore, this optimization based on winding shape and position is simple and feasible, suppressing the CM noise significantly. Compared with conventional multilayer winding structure, this optimization increases the current‐carrying area by 2.8%–5.9%, effectively improving the primary current distribution. In addition, the proposed structure makes the best planar windings in footprint with expanded windings, bringing the simplest layout in the primary winding. Finally, a 1 MHz 400 V/12 V 300 W LLC converter is constructed to verify the effect of this winding structure. The results show that a 40% reduction in CM current can be achieved while maintaining the current balance.

Structural and Magnetic Transformations from CuCl to Cu2Cl(OH)3 Induced by H2O and CuCl2

This study explores the oxidation dynamics of “pure” CuCl during prolonged environmental exposure through X-ray diffraction and temperature-dependent magnetization assessments. While CuCl is traditionally considered diamagnetic, our investigation reveals the emergence of an antiferromagnetic transition at 4.7 K. This anomaly is potentially induced by the integration of water molecules into the CuCl matrix. The hydration process initiates a series of oxidation reactions, ultimately transmuting CuCl into Cu2Cl(OH)3. Over time, the distinctive diffraction pattern peaks corresponding to CuCl diminish, concurrently with the appearance and intensification of those ascribed to Cu2Cl(OH)3, culminating in a complete phase transition as confirmed by X-ray analysis. Correspondingly, magnetization measurements clearly discern magnetic transitions at 6.4 and 16 K, intensifying with the sample’s exposure duration. These findings illuminate the stark potential for probing the magnetic intricacies of Cu2Cl(OH)3, a subject that remains a compelling and unresolved intrigue within the field.

Structural and magnetic transformations in the system YBaCo4O7+X (x = 0, 0.1, 0.2)

The modification of magnetic and elastic properties of YBaCo4O7+x (x = 0, 0.1) cobaltite series at a small controlled deviation x = 0, 0.1, 0.2 from stoichiometry has been investigated. The non-stoichiometric cobaltites with x > 0.1 are found to be separated into two structural phases with different values of x under certain synthesis and heat-treatment conditions of the YBaCo4O7+x system (x = 0, 0.1, 0.2). A non-trivial magnetic behavior is observed in stoichiometric YBaCo4O7. Magnetic moment ΔM = MFC–MZFC induced by an external magnetic field (an analog of thermo-residual magnetization) exhibits anomalies at magnetic phase transition temperatures TN1 and TN2 that coincide with Young’s modulus anomalies. Conversely, in the magnetic susceptibility curves taken in the FC and ZFC modes, phase transitions are not discerned. When x deviates from stoichiometry, the ratio between two magnetic ions Co3+/Co2+ changes, the induced moment ΔM increases, and a residual ferromagnetic moment of ∼ 10-2μB appears in the magnetization curves at low temperatures. At a slight deviation from the oxygen stoichiometry in the samples, the structural distortion disappears, and the anomalies in the elastic characteristics near the TN region rapidly diffuse and vanish. It has been found that when YBaCo4O7+x cobaltites deviate from stoichiometry, the evolution of their magnetic properties is similar to that observed at the transition from Y-based to Ca-based cobaltite. Two scenarios of the cobalt subsystem magnetic behavior with an increasing fraction of cobalt Co3+ ions have been discussed.

Ab initio investigation of electronic structure and magnetic transformation during the bcc to hcp transition in Fe induced by pressure

The pressure-induced structural transition from a body-centered cubic (bcc) to a hexagonal close-packed (hcp) crystal in Fe is studied through ab initio electronic structure calculations, combining with the thermodynamic and kinetic phase-transition methods. According to the energy-volume relationship and thermodynamic criterion, the reasonable phase transition pressure is calculated to be about 13.88 GPa. The SSNEB method is employed to examine kinetic structural and barrier changes along bcc-hcp transition under various pressures. The transformation path involves the deformation of (110)bcc into the tightly packed (0001)hcp, accompanied by the relative slip of (110)bcc along the [1̅10]bcc direction, leading to the formation of the hcp structure. Our results indicate a reduction in the transition barrier of bcc-hcp with increasing pressure. Under the thermodynamic phase transition pressure, the bcc-hcp phase transition barrier is still as high as 140 meV, implying that pure hydrostatic pressure is not a sufficient condition to drive the phase transition. In addition, different from the continuous change of volume, the magnetism of the structure undergoes a magnetic mutation at the transition state, and the phase transition process involves complex magnetic transitions.

Observation of Hydrostatic‐Pressure‐Modulated Giant Caloric Effect and Electronic Topological Transition

AbstractPhase transition is a fundamental phenomenon in condensed matter physics, in which states of matter transform to each other with various critical behaviors under different conditions. The magnetic martensitic transformation features significant multi‐caloric effects that benefit the solid‐state cooling or heat pumping. Meanwhile, the electronic topological transition (ETT) driven by pressure has been rarely reported in martensitic systems. Here, the modulation effects of hydrostatic pressure on phase transitions in a magnetic martensitic alloy are reported. Owing to the huge volume expansion during the transition, the martensitic transition temperature is driven from 339 to 273 K by pressure within 1 GPa, resulting in highly tunable giant baro‐ and magneto‐caloric effects (BCE and MCE) in a wide working temperature range. Interestingly, an ETT is further induced by pressure in the martensite phase, with a sudden drop of the measured saturation magnetization around 0.6 GPa. First‐principles calculations reveal a sharp change in the density of states (DOS) due to the orbit shift around the Fermi level at the same pressure and reproduce the experimental observation of magnetization. Besides, the ETT is accompanied by remarkable changes in the lattice parameters and the unit‐cell orthorhombicity. The study provides insight into pressure‐modulated exotic phase‐transition phenomena in magnetic martensitic systems.

Impact of Cobalt-Doping on the Optical, Magnetic, and Electronic Features of Hexagonal Cadmium Sulfide

CdS and Cd0.9Co0.1S samples were prepared under an N2 atmosphere. The structural analysis was conducted using X-ray diffraction. The structural and microstructure parameters were determined using Rietveld refinement method. The incorporation of cobalt ions into CdS matrix was confirmed by energy-dispersive spectroscopy and Fourier-transform infrared analysis. CdS sample has a non-magnetic feature while the Co-doped sample exhibited a magnetic behavior. The origin of magnetic property transformation has been investigated, revealing the emergence of ferromagnetic ordering and the conversion to a diluted magnetic semiconductor (DMS) with a calculated magnetic moment of 2.56 μ B upon Co doping. We also investigated how this Cobalt-doping-driven transformation affected optical, photoluminescence, and electronic properties. These effects correlated with the emergence of hyper-deep defect states. Electronic properties were calculated using density functional theory (DFT) with the HSE06 hybrid functional approximation. The calculated energy bandgaps for both Co-doped and pure CdS were 2.13 and 2.12 eV, respectively, while experimental measurements from our UV analysis yielded values of 2.26 and 2.15 eV. DFT calculations were employed to explore the magnetic properties, absorption coefficients, refractive indices, real and imaginary dielectric components, and energy loss spectra in both samples.

Glass formation, crystallization behavior, nanoprecipitate phase, and magnetic properties of Mn-Fe-Si-B-EM (EM = Zr, Nb, V) alloys

In this paper, the as-quenched Mn55Fe15Si20B7EM3 (EM = Zr, Nb, V) amorphous ribbons were produced by the melt spinning technique. The crystallization behavior, nanoprecipitate phase evolution, and magnetic properties of the Mn-Fe-Si-B-EM (EM = Zr, Nb, V) amorphous alloys were investigated by X-ray diffraction (XRD), differential scanning calorimeter (DSC), and the quantum design dynacool-9 physical property measurement system (PPMS). The Mn55Fe15Si20B7EM3 (EM = Zr, Nb, V) amorphous alloys show two-stage crystallization behavior. In the first stage, the primary crystallization results in the formation of α-Mn + Mn6Si/Mn3Si precipitates, while in the second stage, the secondary crystallization leads to the formation of the Mn2B phase. The Mn55Fe15Si20B7Zr3 (FZ) amorphous sample shows a most significant two-stage phase transformation, which the onset temperature of the primary and that of the secondary crystallization are 625.7 °C and 681.2 °C, respectively. The FZ amorphous sample undergoes a magnetic phase transformation from the spin glass (SG) state to a paramagnetic (PM) state at approximately 28 K. As the temperature increases, the magnetic phase transition can be expressed as: SG → PM. The annealed FZ nanocrystalline sample with α-Mn + Mn6Si nano phases enters the ferromagnetic (FM) state at 27∼70 K after undergoing spin glass transformation, and the magnetic phase transition is: SG → FM → PM. The annealed Mn55Fe15Si20B7V3 nanocrystalline sample containing nano α-Mn and Mn3Si phases shows two Curie transitions at 57 K and 130 K, respectively. The magnetic phase transition behavior can be expressed as: SG → FMΙ → FMΙΙ → PM.

Cooperatively tuning magnetic anisotropy and colossal magnetoresistance via atomic-scale buffer layers in highly strained La0.7Sr0.3MnO3 films

Achieving simultaneous control over multiple functional properties, such as magnetic anisotropy, magnetoresistance, and metal-insulator transition, with atomic precision remains a major challenge for realizing advanced spintronic functionalities. Here, we demonstrate a unique approach to cooperatively tune these multiple functional properties in highly strained La0.7Sr0.3MnO3 (LSMO) thin films. By inserting varying perovskite buffer layers, compressively strained LSMO films transition from a ferromagnetic insulator with out-of-plane magnetic anisotropy to a metallic state with in-plane anisotropy. Remarkably, atomic-scale control of the buffer layer thickness enables precise tuning of this magnetic and electronic phase transformation. We achieve a colossal magnetoresistance tuning of 10,000% and an exceptionally sharp transition from out-of-plane to in-plane magnetic anisotropy within just a few atomic layers. These results demonstrate an unprecedented level of control over multiple functional properties, paving the way for the rational design of multifunctional oxide spintronic devices.

A novel cost-effective power supply model for industrial appliances based on triangular magnetic shunt transformer design

This paper presents a new design of a magnetic shunt transformer for use in industrial microwave generators. The proposed transformer has a triangular shape and offers several advantages over existing transformer designs, including reduced volume and maintenance costs. We provide a detailed analysis of the transformer's dimensions and an equivalent model of the three-phase high voltage power supply system. The results of this study have significant implications for the field of industrial microwave generator design and could lead to the development of more efficient and costeffective systems. The resulting model is comprised of saturable inductors capable of accounting for the non-linear phenomena of saturation. The power supply is simulated using MATLAB/Simulink with a neuro-fuzzy ANFIS approach. The results are compared to experimental validations of a single-phase reference power supply for a magnetron, validating the proposed power supply. Additionally, the simulation results demonstrate the effectiveness of the proposed design, which outperforms existing transformers in terms of volume, energy efficiency and maintenance costs.