Variation Of Magnetic Properties Research Articles

Powdering and SPS sintering effect on the magnetocaloric properties of MnNiSi-based compounds

Shaping process is crucial for the application of MM′X systems which are commonly fragile due to the large volume effect during phase transition. We adopted spark plasma sintering as a new method to produce MnNiSi-based bulks and investigated the variations of both structural and magnetic properties. The sintering process creates many micro-cracks inside the large particles and changes the residual strain in the small particles. It leads to the reduction of the entropy change, while the relative cooling power is increased by 7%. This work provides reference for further investigations about the effects of different shaping processes on the performance of MM′X systems.

Structural, electrical and magnetic parameters evaluation of nanocrystalline rare earth Nd3+-substituted nickel-zinc spinel ferrite particles

Magnetic nanomaterials have been extensively studied due to their numerous applications in almost all types of electronics as well as in biomedical fields. In this work, Ni0.65Zn0.35NdxFe2-xO4 nanoparticles (0.00 ≤ x ≥ 0.075) have been prepared by co-precipitation method. The structural and electromagnetic properties were tuned by doping of rare earth. The prepared nano-ferrites were annealed in furnace for 5 h at 800 °C. The structural, spectral, magnetic and electrical behavior of Ni0.65Zn0.35NdxFe2-xO4 nanoparticles was investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometery (VSM) and current voltage measurement (I-V) measurements. The objective of this work is to study the variation of magnetic and electric properties as a function of concentration of dopant i.e. rare earth Nd3+ cations. Formation of single phase in all prepared sample except x = 0.075 was confirmed by XRD analysis and estimated crystallite size was 14–26 nm. The lattice parameter, electric properties and magnetic parameters showed non-linear behavior with the doping of Nd+3. Intrinsic metal ion vibrations of spinel ferrites were explained by FTIR spectra recorded in the range of 400–2000 nm. Influence of Nd+3 contents on structural, magnetic, and electrical parameters has been discussed in detail.

Transition metal doping engineered octagonal ZnO monolayer magnetic properties

The two-dimensional (2D) topology assisted direct exchange interaction induced magnetic properties are in principle can be engineered for applications. To this endeavor, density functional theory (DFT) based first principle calculations are performed to study doping of 3d transition metal (TM) in graphene-like hexagonal (h)- and recently proposed octagonal (o)-ZnO monolayers. The o-ZnO monolayer shows high thermal stability (up to 1300 K) along with high energetically doping preference for 3d TM. By virtue of Hund’s rule, the TM doped localized magnetic moment of system can be tuned up to 5 μB based on the choice of TM and type of doping. The general trend of increase in charge transfer and doping stability with decrease in atomic number is found, the exceptions are of Cr and Mn. Doping of Mn, Cr and Fe shows high magnetic moment, among them doping of Fe is energetically most stable. Incorporation of U parameter changes electronic structure landscape significantly but relative variation in magnetic properties remained similar. High doping concentration of Fe prefers antiferromagnetic exchange coupling in order to minimize the system energy while mixing of interstitial along with substitutional doping leads to high magnetic moment as a result of topologically assisted direct exchange interaction. The substitutional doping of TM (except Ti and V) is predicted to be useful for spintronic applications, wherein with the exception of Co, o-ZnO monolayer is found to be a superior candidate than h-ZnO monolayer.

Effect of thermal calcination on the structural, dielectric and magnetic properties of (ZnO–Ni) semiconductor

We report the variations in structural, dielectric and magnetic properties with elevation of calcination temperature of (ZnO, Ni), synthesized by hydrothermal route. Incorporation of Ni in ZnO lattice is accompanied by numerous oxygen vacancies. With increasing calcinations temperature, enhancement in particle size with improvement in crystallization are observed, which is most probably due to grain growth having less number of grain boundaries and enhancement in grain volume. The dielectric behavior gives deep insight of (ZnO, Ni) nanoparticles microstructure. The abrupt increase in A.C. conductivity (σa.c) at high frequencies arises due to the addition of detached charge carrier from trap states to the conduction charge carriers. The (ZnO, Ni) nanoparticles, calcined at different temperatures, show significant changes in the hysteresis loop of ZnO nanoparticles: the loop shows strong ferromagnetic (FM) behavior. The magnetization enhances with increasing the calcination temperature of the particle (Ni, ZnO). Defects (oxygen vacancies) are found to be the main reason for room-temperature ferromagnetism (RTFM) in the (ZnO, Ni) nanoparticles. The enhanced dielectric and magnetic properties of (ZnO, Ni) nanoparticles are strongly correlated with the increase of oxygen vacancies.

Influence of tensile stress on hysteresis loop of Reduced Activation Ferrite & Martensitic steel

The influence of tensile stress on hysteresis loop of Reduced Activation Ferrite & Martensitic steel (RAFM steel) in elastic region was quantitatively evaluated through experiments in this paper. In view of in vessel structures of the RAFM steel in the Tokamak devices, the variation of magnetic material properties caused by forces or mechanical deformation may lead to unexpected influences on their dynamical behaviors, even safety problem. In this paper, tensile experiments of a RAFM steel were conducted under magnetic field up to 60 kA/m to measure its hysteresis loops under different tensile stress. Tensile specimens of a RAFM steel developed in China (CLAM steel) were fabricated and measured with a multi-field coupling experimental system. The maximum relative permeability under different experimental conditions was extracted from the measured hysteresis loops. Experimental results show that a clear variation of the maximum magnetic permeability was observed when the external tensile stress was enlarged. In addition, based on a linear theory of magneto-solid coupling mechanics, a model of constitutive relation between tensile stress and maximum magnetic permeability was put forward and validated based on the experimental results.

Effect of hydrostatic pressure on the magnetic and magnetocaloric properties of Fe-doped MnCoGe alloys

Detailed structural and magnetic investigations have been performed on two equally Fe-doped MnCoGe alloys of nominal compositions Mn0.875Fe0.125CoGe and MnCo0.875Fe0.125Ge. The presence of martensitic phase transition (MPT) in both alloys is clear from the temperature variation of structural and magnetic properties. The nature of MPT is found to be complete in the Mn site Fe-doped alloy. On the other hand, a partial nature of the MPT is observed for the Co site Fe-doped alloy. The application of external hydrostatic pressure hardly affects the magnetic and structural transition temperatures. Both alloys show a significant amount of the magnetocaloric effect in ambient as well as in high pressure situation around their magnetic and structural transition regions.

Effect of cooling rates on the microstructure and magnetic properties of MnAl permanent magnetic alloys

Abstract In this work, the microstructure, phase transformation and magnetic properties of MnAl permanent magnetic alloys prepared by the melt-spinning technique were systematically investigated by tuning the cooling rate. It was shown that the MnAl microstructure, phase transformation and magnetic properties can be tailored by the copper roller speed. With increasing of the roller speed, the phase transformation from the γ2, β phases to the e phase was observed. In addition, the variation of magnetic properties was attributed to the phase content and microstructure of the ferromagnetic τ phase in the MnAl alloys, being controlled by the cooling rate. As a result, the high-purity τ phase MnAl was obtained at a copper roller speed of 5 m/s, which exhibited a high magnetization of 118.2 emu/g. Therefore, this work can provide a method for the direct fabrication of the high-purity ferromagnetic τ phase MnAl alloy.

Physical, structural, morphological, magnetic and electrical properties of Co0.5-xNixZn0.5Fe2O4 nanocrystalline ferrites

A series of Co0.5-xNixZn0.5Fe2O4 (x = 0–0.25 insteps of 0.05) nano crystalline ferrites were synthesized in combustion method using citric acid as fuel. Densities and porosities were calculated using the lattice constant and Archimedes's principle. A linear increase in experimental density and a decrease in porosity were observed with increase in nickel concentration. Cationic distribution was proposed on the basis of theoretical lattice constant and it was correlated with the variation in magnetic and electrical properties of all samples. TEM image of the sample with nickel concentration x = 0.15 indicated the existence of nano-metric range particles and the sample was characterized with the help of inter-planar spacing(s) from SAED pattern. Morphological and surface analysis was studies using Scanning Electron Microscopy and well developed nearly spherical grains were observed with increase in nickel concentration. Energy Dispersive Spectroscopic (EDS) analysis was performed for all nickel substituted samples and all displayed stoichiometric proportions of ions in the samples as per the chemical composition. Elemental mapping was done for all samples using EDS data. Curie temperature was dropped nearly 90 °C at the end of the series. Initial permeability showed slight variation with an increase in nickel concentration and it remained nearly constant with frequency up to 3 MHz. Magnetic loss was observed to be constant for all samples after 100 kHz. DC Electrical resistivities of all samples were measured and all samples displayed resistivity in the order of 108 Ω-cm. AC resistivity and dielectric studies were conducted from 100 Hz to 5 MHz for all samples. Dielectric constant and losses of all samples exhibited very low values compared to that of conventional ferrites. The electrical properties of all samples were discussed with the help of temperature variation of resistivity, activation energy, grain size, density and porosity.

The Influence of Annealing on the Structural and Soft Magnetic Properties of (Fe0.4Co0.6)79Nb₃B18 Nanocrystalline Alloys.

The soft magnetic properties of Fe-based nanocrystalline alloys are determined by their grain size. In the present article, the (Fe0.4Co0.6)79Nb3B18 nanocrystalline alloys have been successfully prepared by isothermal annealing. The variation of soft magnetic properties as a function of annealing temperature and incubation time is investigated in detail. Two distinct crystallization behaviors were found for the (Fe0.4Co0.6)79Nb3B18 alloys. The initial nanocrystallization products comprise a mixture of α-Fe(Co), Fe2B, and Fe23B6-type crystalline metastable phases, and the final crystallization products are composed of α-Fe(Co), Fe2B, and Fe3B crystalline phases. The grain size decreases first and then increases with the increasing annealing temperature in the range of 764–1151 K, and a fine grain size with mean grain size of 12.7 nm can be achieved for alloys annealed at 880 K. As the annealing temperature increases from 764 K to 1151 K, the saturation magnetization increases first and then decreases without a significant increase of the coercivity. The alloys annealed at 880 K exhibit the optimized soft magnetic properties with high Ms of 145 emu g−1 and low Hc of 0.04 Oe.

Magnetic Properties of Deep‐Sea Sediments From the North Pacific: A Proxy of Glacial Deep‐Water Ventilation

AbstractThe magnetic properties of deep‐sea sediments in the North Pacific vary in sync with glacial‐interglacial climatic changes and have thus been considered as a paleoclimate indicator. However, the causes of these variations in magnetic properties, including the concentration, grain size, and mineralogy of magnetic minerals, remain poorly understood. Here we investigate the magnetic properties of deep‐sea sediments recovered from the Shatsky Rise in the North Pacific to investigate the cause of the variability associated with glacial‐interglacial cycles. Compared to the potential sediment provenances, the interglacial‐stage and more than half of the glacial‐stage sediments reveal magnetic mineralogical properties (S ratio and L ratio) of the Gobi and Taklimakan deserts, probably indicating dust from the both sources. During glacials, an abrupt decrease in the concentration of magnetic minerals is associated with increases in the average grain size and in the proportion of hematite relative to magnetite. The changes during glacials are mostly a result of dissolutions of magnetite by exposure to ambient ocean environments after deposition. Both magnetic and geochemical proxies validate that poor ventilation of the glacial deep waters in the North Pacific possibly induced iron‐reducing conditions. With comprehensive compilation with the S‐ratio data in the North Pacific sediments, our result indicates that the poorly ventilated deep waters reached up to water depths of ~2,500 m during glacials.

Structural and magnetic properties variation of manganese ferrites via Co-Ni substitution

Abstract In this study Co-Ni co-doped nanocrystalline manganese ferrites were fabricated via co-precipitation method. The annealing of as prepared nanoferrites was done at 950 °C for 7 h. The powder X-ray diffraction (XRD) confirmed that all samples possessed cubic spinel structure. The crystallite size was determined by Scherrer’s equation that lies in the range of 27–35 nm. The spectral analysis confirmed bending and stretching of bonds at octahedral (B) and tetrahedral (A) sites. The spectral bands were shifted towards the longer wavelength side and these indicate the incorporation of dopants cations (Co-Ni). The magnetic parameters were measured from the M-H loops of nanoferrites. With the increase of Co-Ni contents, the saturation magnetization (Ms) increased up to x = 0.15 and then it decreased. The dielectric properties of all compositions were studied in 1 MHz–3 GHz range and were discussed in the light of Debye-type reduction phenomenon by following the Koop’s theory. The dielectric and magnetic behavior evaluation suggested that synthesized ferrites are suitable for microwave devices fabrication.

Simulation of temperature distribution in the oriented silicon steel coil in the heating stage of annealing process

Annular furnace is widely used for high temperature annealing of oriented silicon steel coils. The coils are placed under a cover in a protective atmosphere. The heating rate of the process must be strictly controlled to prevent magnetic property variations of the products. In this work, temperature distribution in the coil at the heating stage is simulated using finite method. Effects of fuel flux at burners on temperature distribution in the furnace are also analysed. Experiments are carried out to measure the parameters needed in simulations and to verify the simulation results. For a coil of 510 mm inside and 1710 mm outside diameters, the largest temperature difference in the coil is found to be as high as 438 °C, which occurs at about 8 h of heating. A total of 72 h is needed for the temperatures across the coil to reach a target level of 1170 °C. The temperature difference in the coil can be greatly reduced if N2 is replaced by H2 as protective atmosphere and the gap between sheet layers in the coil is reduced. Temperature distribution on the cover during heating is found to be rather uniform with the largest difference being within 30 °C.

Variations of energy band gap and magnetic properties upon quantum confinement effects on the Cr doped ZnO nanoparticles

In this paper, Cr doped ZnO nanoparticles with different at % ratio (0, 2, 4, 6, 8, 10) (NPs) were synthesized with a precipitation method in ethanol. The synthesized nanoparticles have been analyzed using thermogravimetric analysis (TGA), x-ray diffraction (XRD), Energy dispersive x-ray spectroscopy (EDXS), transmission electron microscope (TEM), UV–vis spectrometer and Vibrating sample magnetometer (VSM) measurements. The XRD studies showed that the phase singularity of ZnO wurtizte hexagonal type structure. The surface morphology investigations by TEM confirmed the reduction of the particle size with increasing Cr content estimated from Williamson-Hall analysis of the diffraction peaks. The analysis of the UV–vis spectra of Cr doped NPs reveals that the wavelength of the absorption maxima λmax blue shifted to lower wavelength with increases the Cr content indicating the decrease in the particle size and recommends the increasing of energy gap with Cr content into ZnO semiconducting NPs. The observed increase of the energy band gap of Cr-doped ZnO nanoparticles caused by the decrease in the particle size with Cr concentration is attributed to the quantum confinement effect. The magnetization measurements showed room temperature ferromagnetism for all synthesized nanoparticles which can be attributed to the carrier-mediated exchange interaction improved by intrinsic defects.

Synthesis of ferrimagnetic/ferroelectric composite and its magnetic and electrical characterization

The composites were synthesized using the nanoparticles of Mn0.5Zn0.5Fe2O4 and BaTiO3 via solid state route. The X-ray diffraction pattern and microstructure of the composite samples confirm the coexistence of ferroelectric and ferrimagnetic phases. The magnetization is found to increase through the inclusion of ferrite. The ferrimagnetic/ferroelectric composites show a decrease in dielectric constant value with an increase in dielectric loss by increasing ferrite-content. The variation of magnetic and dielectric properties also confirms the coexistence of ferrimagnetic and ferroelectric phase.

A simple method for tuning perpendicular magnetic properties of ultra-thin TbFeCo films

Ultra-thin amorphous TbFeCo films with perpendicular magnetic anisotropy (PMA) are sputtered. The PMA of the alloy films is found to be strongly related to the thickness. A critical thickness is observed to exist, where a transition from a FeCo-dominant to a Tb-dominant configuration occurs. Large variation of magnetic properties is demonstrated for the film in the thickness range across this critical thickness. Our results show the critical thickness may be used as an alternative way to tune the perpendicular magnetic properties of the ultra-thin TbFeCo films.

Potential of open source simulation tools for induction heating

The paper describes simulation of induction heating process of ferromagnetic steel, when a full non-linear model is used: a temperature dependent B-H curve is taken into account. The full B(H,T) model is essential to obtain accurate results, which are confirmed by experimental validation. The paper also points out sensitivity of the model to slight variation of magnetic properties of material like Curie temperature, which might vary for steel of different grades. All results in the paper are obtained using open source simulation tools that demonstrates high accuracy compared to experimental results and benchmarked commercial software ANSYS Classic.

Domain wall characterization inside grain and around grain boundary under tensile stress

Stress measurement is an important field of non-destructive testing and evaluation (NDT&E). This can ensure stability and structural rigidity of workpieces. The challenging task of stress measurement is the properties characterization of the microscopic magnetic, especially the microstructure at different location of grains. The qualitative analysis of magnetic properties variation under low stress inside grain and around grain boundary are difficult to be obtained with a reliable solution. This paper investigates characters of the domain wall inside grains and around grain boundaries under low tensile stress. The domain walls of the silicon steel sheet are captured by the magneto-optical Kerr effect (MOKE) microscopy. The stress changes the magneto-elastic energy and the angle between magnetization and stress. The relationship among domain wall, magneto-elastic energy, the magnetization inside grains and around grains boundaries under different tensile stress is provided and analyzed in details. Magnetization work calculates the energy required for magnetization to quantify the difference of the magnetic domains distribution caused by increment of magneto-elastic energy under different tensile stress in different locations. The difference of magnetization work in these locations is highly affected by the tensile stress. This proposed work has the potential to evaluate the effect of grain and grain boundary on stress measurement.

Changing sediment sources in the Bay of Bengal: Evidence of summer monsoon intensification and ice-melt over Himalaya during the Late Quaternary

A gravity core retrieved from the southern Bay of Bengal (BoB) was studied to determine the sources of sediments and factors controlling their distributions during the Late Quaternary. The parameters used for this study was sediment grain size, organic carbon, clay mineralogy and environmental magnetic properties. Radiocarbon ages of sediments indicate that the 3.06 m long sediment core covers a period since ~45 cal kyr B.P. The sediments deposited before ~14 cal kyr B.P. were clayey silt with higher magnetic susceptibility (MS) values (av: 26 × 10−8 m3 kg−1) and those deposited after ~14 cal kyr B.P. were sandy silt with lower MS values (avg: 13 × 10−8 m3 kg−1). The latter period (after ~14 cal kyr B.P.) indicated high energy turbidites from the Himalayan Rivers into the BoB due to the strengthening of summer monsoon and ice-melt in the Himalayas. Higher smectite and lower illite contents during the last glacial maximum (LGM) reflected low sediment supply from the Ganges-Brahmaputra River System (GBRS) and higher illite and lower smectite during ~14 cal kyr B.P. indicated increased sediment supply from GBRS during this interglacial period. The magnetic grain size of sediments deposited from ~15 cal kyr B.P. was more fine-grained at the start of the Bølling-Ållerød (B-A) event and coarse-grained during ~13 cal kyr B.P. (Younger Dryas event). Fine-grained magnetic minerals also showed a peak at ~11 cal kyr B.P. along with higher summer solar insolation. The down-core variations in sediment grain size, magnetic properties and clay minerals were interpreted in relation to the significant changes in sources of sediments in the BoB during different climatic events. The changing sediment supply in the BoB was due to the combined influence of ice-melt by increased solar insolation and intensification of summer monsoon over Himalaya. Increase of fine-grained magnetic minerals at ~15 cal kyr B.P. and coarser sediment fraction at ~14 cal kyr B.P. indicated time gap between intensification of summer monsoon and ice-melt over Himalaya, respectively. The trend of the magnetic grain size record seems to be modulated by orbital-scale variations in June insolation, which coincides with the summer monsoon variations also. These observed climatic variations are correlating well with the climate changes of the Northern Hemisphere during the Late Quaternary.

Nanoscale magnetic localization in exchange strength modulated ferromagnets

Although ferromagnetism is in general a long-range collective phenomenon, it is possible to induce local spatial variations of magnetic properties in ferromagnetic materials. For example, systematic variation of the exchange coupling strength can be used to create systems that behave as if they are comprised of virtually independent segments that exhibit "local" Curie temperatures. Such localization of thermodynamic behavior leads to boundaries between strongly and weakly magnetized regions that can be controllably moved within the material with temperature. The utility of this interesting functionality is largely dependent on the inherent spatial resolution of magnetic properties - specifically the distance over which the exchange strength and corresponding properties behave locally. To test the degree to which this type of localization can be realized in materials, we have fabricated epitaxial films of Co[1-x]Ru[x] alloy featuring a nanometer scale triangular wave-like concentration depth profile. Continuous nanoscale modulation of the local Curie temperature was observed using polarized neutron reflectometry. These results are consistent with mean-field simulations of spin systems that encompass the possibility of delocalized exchange coupling, and show that composition grading can be used to localize magnetic properties in films down to the nanometer level. Since this is demonstrated here for an itinerant metal, we assert that for virtually any modulated magnetic material system, collective effects can be suppressed to length scales smaller than about 3 nm, so that magnetic behavior overall can be well described in terms of local material properties.

Multi-scale analysis of strain-dependent magnetocrystalline anisotropy and strain-induced Villari and Nagaoka-Honda effects in a two-dimensional ferromagnetic chromium tri-iodide monolayer

This paper analyzes the magnetic properties of the emerging ferromagnetic chromium tri-iodide (CrI3) monolayer, under compressive and tensile biaxial strains. By combining first-principles density functional theory and Metropolis Monte Carlo methods, the multi-scale simulations are used to quantitatively analyze the strain-dependent magnetocrystalline anisotropy energy, Heisenberg isotropic symmetric exchange effects, anisotropic symmetric exchange effects, magnetic moment, and Curie temperature (Tc). The Villari effect (or the inverse magnetostrictive effect) and the Nagaoka-Honda effect (or the inverse Barret effect) are unraveled. It is shown that a small strain (e.g., smaller than 1%) could change Tc by only less than 1 K. By contrast, a small strain can noticeably influence the hysteresis curve shape and significantly alter the coercive magnetic field (Bc), which offers one of the possible explanations of the large variation of Bc as measured on the strain-prone exfoliated CrI3 monolayers. This also indicates the importance to vanish strain to ensure small device-to-device variation of magnetic properties in the monolayer-based spintronics memory and logic devices. It is revealed that strain can induce changes on a series of key magnetic properties (e.g., the strain-induced magnetization direction flip, the strain-induced ferromagnetic/antiferromagnetic transition, the strain-induced change of magnetic coercivity, etc.), which might be useful to enable monolayer-based sensor applications.