Variation Of Magnetic Properties Research Articles

Should the mass of a nanoferrite sample prepared by autocombustion method be considered as a realistic preparation parameter?

Detectable variations in structural, elastic and magnetic properties have been reported depending on the mass of the cobalt nanoferrite sample prepared by citrate autocombustion method. Heat released during the autocombustion process and its duration are directly proportional to the mass to be prepared, and is thus expected to affect both the crystallite size and the cation distribution giving rise to the reported variations in microstrain, magnetization, and coercivity. Formation of a pure spinel phase has been validated using X-ray diffraction patterns (XRD) and Fourier-transform infrared (FTIR) spectra. Crystallite sizes obtained from Williamson-Hall (W-H) method range from 28–87nm, being further supported by images of high-resolution transmission electron microscope (HRTEM). Saturation magnetization and coercivity deduced from M-H hysteresis loops show a clear correlation with the cation distribution, which was proposed on the basis of experimentally obtained data of XRD, VSM, and IR. Elastic parameters have been estimated using the cation distribution and FTIR data, with a resulting trend quite opposite to that of the lattice parameter.

Electromagnetic properties of nanocrystalline Al3+ substituted MgCuMn ferrites synthesized by microwave hydrothermal method

The effect of Al3+ substitution on electromagnetic properties has been studied for nanocrystalline Mg0.8Cu0.2Mn0.05Al x Fe1.95−x O4 ferrites, wherein x varies from 0 to 0.4 in steps of 0.1. These ferrites were synthesized by using microwave hydrothermal method and then characterized using X-ray diffractometer (XRD), Fourier transform infrared and transmission electron microscopy. The synthesized powders were densified using microwave sintering method at 950∘C/50 min. Structural and surface morphology of sintered samples were characterized using XRD and atomic force microscopy, respectively. The complex permittivity and permeability properties were measured over a frequency range 100 Hz–1.8 GHz. The temperature variation of magnetic properties were measured in the temperature range of 300–650 K. The electrical and magnetization studies inferred that the values of d.c. resistivity increases by 27%, whereas saturation magnetization decreases linearly from 38.6 to 23.0 emu g−1 and Curie temperature was found to be decreased from 628 to 513 K with an increase of Al3+ ions. The low dielectric, magnetic losses, moderate saturation magnetization and high-temperature stability properties exhibited by Al3+ substituted MgCuMn ferrites make them find applications in microwave devices, such as circulators and isolators etc. The applicability of present samples for microwave devices has been tested by the measurement of ferromagnetic resonance linewidth at Ka band.

Structural, morphological and magnetic properties variation of nickel-manganese ferrites with lithium substitution

Mixed ferrites with nominal chemical compositions LixNi0.2Mn0.8−2xFe2+xO4 ranging from x=0 to 0.4 in the steps of 0.1 have been prepared by the auto combustion technique. The X-ray diffraction patterns consist of major cubic spinel LixNi0.2Mn0.8−2xFe2+xO4 phase with minor impurity phases (Fe2O3 and MnO) and with Li substitution phase purity has increased, such that for x=0.4 pure phase spinel structure has been obtained. The lattice parameter has decreased with the increase in Li content obeying Vegard’s law. Both the bulk density and theoretical density have decreased with Li content and with sintering temperature (Ts) up to 1300°C ρB has increased and beyond that it has decreased. Morphological studies have performed by a high resolution optical microscope and observed that average grain size noticeably dependent on Li substitution. The initial permeability (μi′′) has found to decrease with Li substitution. The Curie temperature (TC) has determined from the temperature dependent μi′′ and found to increases with Li content. From the room temperature magnetization measurement, it has observed that all samples are in ferrimagnetic state at room temperature. The number of Bohr magneton has been obtained from the observed saturation magnetization. Dielectric constant, dielectric loss tangent, ac conductivity and complex impedance are studied in the frequency range 20Hz–10MHz. Frequency dependence of dielectric constant in lower frequencies indicates a usual dielectric dispersion due to the Maxwell-Wagner type interfacial polarization. Dielectric loss tangent shows similar behavior like dielectric constant. The complex impedance analysis has been used to study the effect of grain and grain boundary on the electrical properties and with Li content both grain and grain boundary resistance show an increasing trend. The ac conductivity shows frequency independent behavior at the low frequency side and with increasing frequency the conductivity increases.

Magnetic Properties of Thermally Aged Fe-Cu Alloys with Pre-deformation

Magnetic properties of thermally aged Fe-Cu alloys with pre-deformation have been evaluated to improve the understanding of using magnetic technology for the nondestructive evaluation (NDE) of irradiation embrittlement in reactor pressure vessel (RPV) steels. Fe-Cu alloys with and without pre-deformation were thermally aged at 500 °C and the changes in microstructure, mechanical properties and magnetic properties were determined. It is found that the strain-induced dislocations recover and the Cu-rich particles precipitate during the aging process, and the magnetic properties variation depends on the combined influence of these two factors. From the point of view of NDE, a fully tempered or annealed microstructure is favorable before RPV is put into service. These results improve the understanding of magnetic property evolution in actual RPV steels and help to develop NDE theory for irradiation embrittlement.

Mg doping effect on the magnetic properties of Y-type hexaferrite Ba0.5Sr1.5Zn2−xMgxFe12O22

The microstructure and magnetic properties of Mg-doped Ba0.5Sr1.5Zn2Fe12O22 hexaferrites synthesized by the solid state method are investigated. All the undoped and doped samples show a sharp screw proper spin phase to collinear ferrimagnetic spin phase transition above room temperature, and transition temperature increases distinctly with Mg doping. It is noteworthy that all the samples exhibit another magnetic phase transition at a lower temperature T1, which is associated with the longitudinal conical to the proper screw phase transition. The transition temperature T1 can be modulated by varying Mg content, indicating that the longitudinal conical spin phase is stabilized by the Mg-substitution. The saturation magnetization at room temperature increases to a maximum with Mg content x = 0.8 and then decreases with x. The variations of magnetic properties can be ascribed to the difference in the preferential site for Zn and Mg and different distribution of Fe3+ ions over tetrahedral and octahedral sites. It is worth noting that the range for the intermediate-III phase increases significantly as x increases to 2.0, suggesting that Mg-doped samples may be display field-induced ferroelectric order at temperature close to RT and in wide magnetic-field regions. The room-temperature M-H curves at lower applied field indicate that magnetic-field-induced ferroelectric phase can be stabilized at zero magnetic field by the substitution by Mg2+ for Zn2+. The Mg-doped hexaferrites Ba0.5Sr1.5Zn2Fe12O22 may be potential candidates for applying in magnetoelectric devices.

Study on Proton Radiation Resistance of 410 Martensitic Stainless Steels under 3 MeV Proton Irradiation

In this study, we report on an investigation of proton radiation resistance of 410 martensitic stainless steels under 3 MeV proton with the doses ranging from <TEX>$1.0{\times}10^{15}$</TEX> to <TEX>$1.0{\times}10^{17}p/cm^2$</TEX> at the temperature 623 K. Vibrating sample magnetometer (VSM) and X-ray diffractometer (XRD) were used to study the variation of magnetic properties and structural damages by virtue of proton irradiation, respectively. VSM and XRD analysis revealed that the 410 martensitic stainless steels showed proton radiation resistance up to <TEX>$10^{17}p/cm^2$</TEX>. Proton energy degradation and flux attenuations in 410 stainless steels as a function of penetration depth were calculated by using Stopping and Range of Ions in Matter (SRIM) code. It suggested that the 410 stainless steels have the radiation resistance up to <TEX>$5.2{\times}10^{-3}$</TEX> dpa which corresponds to neutron irradiation of <TEX>$3.5{\times}10^{18}n/cm^2$</TEX>. These results could be used to predict the maintenance period of SUS410 stainless steels in fission power plants.

Compositional variation of structural, electrical and magnetic properties of Dy substituted Ni–Co spinel ferrite

In the present work nanocrystalline dysprosium substituted Ni0.8Co0.2Fe2−xDyxO4 (x = 0.00, 0.025, 0.050, 0.075 & 0.1) ferrite system was synthesized by the solution combustion method. The phase formation has been confirmed by Reitveld analysis of XRD patterns, which is a characteristic of spinel ferrite with most intense (311) peak. The bond lengths and site radii of tetrahedral and octahedral sites are found to increase with increase in Dy content. IR measurements showed two prominent bands which are common characteristics of spinel ferrite. The surface morphology shows spherical grains of increasing size with increase in Dy content. The dielectric measurements show the usual dielectric dispersion due to space charge polarization. The electrical resistivity of Ni–Co ferrites is found to increase with Dy content. This can be explained on the basis of formation of DyFeO3 secondary phase along with spinel lattice. Complex impedance spectra show incomplete semicircles due to the high resistance values at low frequency. Magnetic measurements reveal low coercive field with increase in Dy content. Low coercive fields suggest the use of these materials in data storage and magnetic shielding devices.

Structural, optical, and ferromagnetic characterization of Sm-doped LaOCl nanocrystalline synthesized by solvothermal route: Significant effect of hydrogen post treatment

Pure and Sm-doped lanthanum oxychloride (LaOCl) nanomaterials were synthesized by solvothermal route followed by a subsequent heat treatment process. The objective of the present work is to study and develop conditions required to create stable room-temperature ferromagnetic (RT-FM) properties in LaOCl. To achieve that aim, magnetic samarium Sm3+ ions were used as dopant sources for stable FM properties. Systematic structural, optical, and magnetic properties of undoped and Sm-doped LaOCl samples were investigated as function of post-annealing conditions (temperature and atmosphere). The optical absorption properties were studied by diffuse reflection spectroscopy (DRS). The magnetic measurements reveal that Sm-doped LaOCl nanopowders have partial RT-FM properties due to the doped ions. The variations of magnetic properties with pre-annealing temperature were investigated. Furthermore, the electronic medium of host LaOCl crystalline lattice, which carries the spin-spin (S.S) exchange interaction between localised dopant Sm3+(4f5) spins, was developed by annealing in hydrogen gas (hydrogenation). It was established that annealing in hydrogen atmosphere boosts the RT-FM properties so that the saturation magnetisation could be increased by more than 100%. Physical explanations and discussions were given in this paper. Thus, it was proved that the magnetic properties could be tailored to diamagnetic LaOCl compound by Sm-doping and post treatment under H2 atmosphere. Therefore, LaOCl nanocrystals could be used as a potential candidate for optical phosphor applications with magnetic properties.

Electrodeposition of Nanostructured Permalloy and Permalloy-Magnetite Composite Coatings and Investigation of Their Magnetic Properties

Permalloy and permalloy-magnetite coatings were electrodeposited with the average thickness of 100 µm with certain operating parameters, such as the current density of 100 mA/cm2, pH 3.8, and the temperature of 298 K (25 °C), to fabricate alloy and composite coatings, respectively. The aim was to promote the magnetic properties of permalloy coating in order to extend its magnetic applications. For this purpose, nanocrystalline permalloy and permalloy-magnetite coatings were electrodeposited. The effect of the content of magnetite particles in the bath on magnetic properties of the samples was investigated. Vibrating sample magnetometry was performed to investigate the variation of magnetic properties of the coatings. The optimum amount of magnetite (2 g/L) was determined according to the highest amount of saturated magnetization and a sensible amount of coercivity. The morphology, phase, elemental analyses of the coatings and the chemical composition analysis of the bath were performed by scanning electron microscopy, X-ray diffraction pattern, quantometry, energy-dispersive X-ray spectroscopy, and ultraviolet–visible spectroscopy. The magnetization was increased initially and then decreased (after a limited amount of magnetite) by enhancing the content of magnetite particles in the bath. Also, the coercivity was decreased by increasing the amount of magnetite particles in the coatings, which was due to the reduction of the grain size of the permalloy matrix.

Variations of magnetic properties of UH3 with modified structure and composition

Abstract UH3 based hydrides with modified structure and composition can be prepared using high H2 pressures from precursors in the form of rapidly cooled uranium alloys. While the alloys with α-U structure lead to the β-UH3 type of hydrides, γ-U alloys (bcc) lead either to α-UH3 hydride type or nanocrystalline β-UH3. The nanocrystalline β-UH3 structure, appearing for Mo alloying, can accommodate in addition numerous other d-metal components, as Ti, Zr, Fe, Nb. The pure Mo alloyed hydrides (UH3)1−xMox exhibit increasing Curie temperature TC with maximum exceeding 200 K for x = 0.12–0.15. Other components added reduce the TC increment with respect to pure UH3 (170 K). Also alloying by Zr gives a weaker enhancement. Seen globally, the TC variations are rather modest, which reflects the prominence of interaction of U with H. It is suggested that important ingredient is a charge transfer, depopulating the U-6d and 7s states, while the 5f band stays at the Fermi level.

Temporal and spatial variations in magnetic properties of suspended particular matter in the Yangtze River drainage and their implications

As the largest river of China, the Yangtze River transports large amounts of sediments to the adjacent oceans. Provenance of these ancient marine sediments can only be deciphered when the source-to-sink process of modern sediments in the Yangtze River is fully understood. Many methods have been used to study the provenance of river sediment and an environmental magnetic method is applied in this study because of its fast, nondestructive advantages. Magnetic properties of suspended particulate matter (SPM) along the Yangtze River were measured to provide a holistic understanding about magnetic properties of sediments in this river and its controlling factors. The results indicate that the dominant magnetic mineral in SPM is magnetite, with a small contribution of hematite and goethite. Significant spatial variation was observed in most of the magnetic parameters, which primarily reflects the distribution of major geologic units along the drainage area of the river. Anthropogenic influences are also recorded in the magnetic parameters. The Three Gorges Dam results in a dramatic decrease of magnetic minerals in the downstream reaches, since its construction in 2003. In addition, small variations in magnetic properties of SPM are found along water depth, together with a clear seasonal shift at Datong station. This seasonal variation of magnetic properties of SPM is driven by variability in both hydrology and source contributions. This complicates the use of magnetic parameters for provenance studies. Magnetic properties of sediments in rivers are capable of tracing provenance areas, but caution must be taken into account.

Ferromagnetism in 5f-band metamagnet UCoAl induced by Os doping

UCoAl is a 5f-band metamagnet with a uniquely low paramagnetic-to-ferromagnetic transition field, 0.7 T, extremely sensitive to any perturbation such as elemental substitution. Here, we study variations of magnetic properties in the UCoAl-UOsAl system on single- and polycrystalline samples with different concentration of Os. We found that osmium can substitute Co in UCoAl up to 20%, while preserving the ZrNiAl structure type. Pure UOsAl was identified as a hexagonal Laves phase, MgZn2 type. It is a weak Pauli paramagnet. Even a 2%-substitution of Os for Co in the 5f band metamagnet stabilizes ferromagnetism with the Curie temperature TC = 26 K and uranium magnetic moment μU = 0.4 μB and shifts the critical metamagnetic field to zero. Higher Os concentrations enhance both TC and μU. All magnetic response is concentrated into the c-axis; the susceptibility for magnetic field perpendicular to c is low and practically temperature-independent. Our study reflects the decisive role of the 5f-5d hybridization in the magnetism of the UCoAl-UOsAl system. This work completes the study of the alloying of UCoAl with late transition metals and indicates that the non-magnetic phase exhibiting band metamagnetism is very limited in the concentration range.

Abnormal variation of magnetic properties with Ce content in (PrNdCe)2Fe14B sintered magnets prepared by dual alloy method**Project supported by the National Natural Science Foundation of China (Grant Nos. 51461033, 51571126, 51541105, and 11547032), the Natural Science Foundation of Inner Mongolia, China (Grant No. 2013MS0110), and the Inner Mongolia University of Science and Technology Innovation Fund, China.

Resource-saving (PrNdCe)2Fe14B sintered magnets with nominal composition (PrNd)15−xCexFe77B8 (x = 0−10) were prepared using a dual alloy method by mixing (PrNd)5Ce10Fe77B8 with (PrNd)15Fe77B8 powders. For Ce atomic percent of 1% and 2%, coercivity decreases dramatically. With further increase of Ce atomic percent, the coercivity increases, peaks at 6.38 kOe in (PrNd)11Ce4Fe77B8, and then declines gradually. The abnormal dependence of coercivity is likely related to the inhomogeneity of rare earth chemical composition in the intergranular phase, where PrNd concentration is strongly dependent on the additive amount of (PrNd)5Ce10Fe77B8 powders. In addition, for Ce atomic percent of 8%, 7%, and 6% the coercivity is higher than that of magnets prepared by the conventional method, which shows the advantage of the dual alloy method in preparing high abundant rare earth magnets.

Variation in magnetic and structural properties of Co-doped Ni–Zn ferrite nanoparticles: a different aspect

Cobalt-substituted nickel–zinc ferrite nanoparticles (Ni0.6−x Zn0.4Co x Fe2O4) (x = 0, 0.0165, 0.033, 0.264 and 0.528) have been synthesized and characterized with respect to their structural and magnetic properties. Exceptionally in spite of the reported literature where the saturation magnetization increases with Co doping that attributes to Co2+ ions distribution in octahedral sites, the saturation magnetization in our samples decreases by increasing Co contents as revealed by vibrating sample magnetometer measurements. To know the structural properties such as phase identification, measurement of crystallite size and other structural parameters, prepared samples have been performed by X-ray diffraction technique. The X-ray diffraction spectra measurements show that samples have single-phase spinel cubic structure at x = 0, 0.033, 0.264 and 0.528, and at x = 0.0165, there is partial formation of hematite phase. The uncommonly decreased saturation magnetization, variation in retentivity, coercivity and magneto-crystalline anisotropy and also variation in structural properties with Co doping are explained on the basis of Co2+ ions distribution in tetrahedral and octahedral sites in place of Ni2+ and Zn2+ ions having different magnetic moments and different ionic radii, respectively. Using transmission electron microscopy, the particles size has been calculated. The morphology and stoichiometry of prepared samples have been investigated by field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy techniques, respectively. The structural and magnetic measurement results are well co-related with each other with respect to Co2+ ions doping and its distributions. The moderate saturation magnetization and low coercivity values of all samples show soft magnetic behavior and attribute the usefulness of these materials in magnetic recording devices.

Variations of phase constitution and magnetic properties with Ce content in Ce-Fe-B permanent magnets

Magnetic materials of Ce12+xFe82−xB6 (x=0, 0.5, 1, 1.5, 2, and 3) containing mainly Ce2Fe14B phase were prepared by melt spinning method. The coercivity is the lowest in Ce12Fe81B6 ribbons. With the increase of Ce content, the coercivity increases monotonically, and X-ray techniques show that the amount of minor phase Fe3B decreases but the amount of CeFe2 increases. Magnetization reversal and magnetic properties are dependent on the amount of minor phases. The squareness of hysteresis loop is the best in Ce13.5Fe80.5B6 ribbons with energy product of 6.80MGOe. Optimizing the phase constitution is necessary to improve magnetic properties in Ce-based alloys for utilizing the rare earth resource in a balanced manner.

Magnetic properties of sediments of the Red River: Effect of sorting on the source‐to‐sink pathway and its implications for environmental reconstruction

AbstractWe conducted a mineral magnetic study of river bank and subaqueous delta sediments from the Red River, in order to examine the role of sedimentary sorting on the variation of sedimentary magnetic properties from source to sink. The magnetic mineralogy mainly consists of magnetite and hematite. Bulk sediment particle‐size variations have a strong influence on magnetic properties, with the frequently used magnetic parameters χfd%, χARM, χARM/χ, and χARM/SIRM exhibiting positive correlations with the &lt;4 µm fraction, while S‐ratios are negatively correlated with this fraction. Compared with river bank sediments and shallow shoreface (&lt;5 m water depth) sediments, sediments from the deeper (&gt;5 m water depth) part of the subaqueous delta have lower χ and SIRM values, a finer ferrimagnetic grain‐size and higher proportions of hematite, consistent with selective loss of coarse ferrimagnetic grains on the source‐to‐sink pathway. We suggest that variations in magnetic properties in response to particle‐size compositions and therefore depositional environment changes should be carefully addressed when magnetic proxies such as χARM/SIRM are used in the study of coastal and marine environmental changes (e.g., sea‐level change). In such cases, the combined use of magnetic properties and geochemical indicators, such as Al/Ti ratio, may provide better results for paleoenvironmental reconstruction.

Structural, Magnetic, and Dielectric Properties of Ni0.5Zn0.5Al x Fe2−x O4 Nanoferrites

This work investigates the effect of non-magnetic aluminum (Al) substitution in structural, morphological, magnetic, and dielectric properties of nanosized Ni0.5Zn0.5Al x Fe2−x O4 (0.0 ≤ x ≤ 0.25) synthesized through citrate-gel autocombustion route (CGAC). Structural characterizations were performed by using X-ray powder diffraction (XRD), FT-IR, and scanning electron microscope (SEM). XRD reveals the formation of single-phase cubic spinel with crystallite sizes around 62–57 nm for all Al substituted samples estimated from Williamson-Hall method. Two significant absorption bands around 600 cm−1 and 400 cm−1 are observed from FT-IR spectra of samples under investigation, which confirms the formation of a single-phase cubic spinel. Interionic bond lengths and bond angles confirm the solubility of Al in the spinel lattice and support the observed variation in magnetic properties. Using vibrating sample magnetometer (VSM) saturation magnetization, coercivity has been measured. A decrease in lattice parameter, saturation magnetization with increasing Al concentration was attributed to the difference in the ionic radii and weakening of exchange interactions. The decrease in initial permeability explained on the basis of variation in grain size and porosity. Dielectric constant and dielectric loss decreases with increasing Al concentration and with frequency.

Composition-dependent variation of magnetic properties and interstitial ordering in homogeneous expanded austenite

The crystal structure and magnetic properties of austenitic stainless steel with a colossal interstitial content, so-called expanded austenite, are currently not completely understood. In the present work, the magnetic properties of homogeneous samples of expanded austenite, as prepared by low-temperature nitriding of thin foils, were investigated with magnetometry and Mössbauer spectroscopy. At room temperature, expanded austenite is paramagnetic for relatively low and for relatively high nitrogen contents (yN = 0.13 and 0.55, respectively, where yN is the interstitial nitrogen occupancy), while ferromagnetism is observed for intermediate nitrogen loads. Spontaneous volume magnetostriction was observed in the ferromagnetic state and the Curie temperature was found to depend strongly on the nitrogen content. For the first time, X-ray diffraction evidence for the occurrence of long-range interstitial order of nitrogen atoms in expanded austenite was observed for high nitrogen contents.

Structure and Magnetic Properties of (001) Oriented CoPt-Ag and CoPd-Ag Alloy Films

20-nm-thick (CoPt)100–xAgx and (CoPd)100–xAgx (001) films (x = 0–20) were grown on MgO(001) substrate at a temperature of 300uC by molecular beam epitaxy, and their crystal structure and magnetic properties were compared with those of FePt-Ag and FePd-Ag films [Y. Tokuoka et al.: J. Appl. Phys., 115, 17B716 (2014)] for the systematic study of the effect of Ag addition into transition metal – noble metal alloy films. For the CoPt-Ag, the addition of 5% Ag increased perpendicular magnetic anisotropy (PMA) and coercivity. However, for the CoPd-Ag, Ag addition enhanced neither the PMA nor the coercivity. Structural analysis of the CoPt-Ag and CoPd-Ag films revealed that Ag addition promoted L10 phase ordering for CoPt-Ag, while L10 ordering was not found in CoPd-Ag. Although there were some similarities in the effect of Ag addition between CoPt-Ag and FePt-Ag, such as increased PMA, coercivity, and L10 ordering, there were different trends in PMA and L10 ordering between CoPd-Ag and FePd-Ag, except that both films showed reduced coercivity with Ag addition. Ag segregation and L10 ordering are considered important factors to explain the variations of structure and magnetic properties with Ag addition.

Breaking the geometric magnetic frustration in controlled off-stoichiometric LuMn1+zO3+δ compounds.

This study explores controlled off-stoichiometric LuMn1+zO3+δ (|z| < 0.1) compounds, intended to retain the utter LuMnO3 intrinsic hexagonal symmetry and ferroelectric properties. X-ray powder diffraction measurements evidenced a single phase P63cm structure. Thermo-gravimetric experiments show a narrow impact of oxygen vacancies while a distinguishable gas exchange at ∼700 K, a surprisingly lower temperature when compared to perovskite systems. A comparison of different nominal ceramics revealed pertinent structural and magnetic property variations owing to subtle self-doping effects. Deviations from the archetypal antiferromagnetic state were detected below ∼90 K suggesting local rearrangements of the nominal Mn(3+) ions matrix, breaking the ideal geometrical spin frustration, leading to a non-compensated magnetic structure.