Variation Of Magnetic Properties Research Articles

Variation of microwave magnetic properties for thin films of ferromagnetic metals with the film thickness

An investigation of the dependence of magnetic properties on the thickness of ferromagnetic films was completed. The study dealt with magnetostatic and microwave measurements of single-layer films of ferromagnetic metals (Fe, Co) and was aimed at revealing reasons for the deterioration of microwave magnetic performance with an increase in film thickness. Two types of variation of microwave permeability with the film thickness were distinguished for the films under study. One exhibited a noticeable deviation from maximal values and was observed for Co. The other case involved a gradual worsening of performance, and was observed for Fe. In the first case, the resonance frequency shifted lower when the film was thicker than 0.2–0.4 μm, and Acher’s coefficient fell by the factor of three. In the second case, the microwave performance worsened gradually, and a decrease of Acher’s coefficient was not large, approximately by 20%. The data analysis showed that the reason for the deterioration is an increase of out-of-plane anisotropy in the first case and sufficient growth of damping factor in the second case.

Conduction mechanism and magnetic behavior of Cu doped barium hexaferrite ceramics

M-type barium hexaferrite ceramics (BaM) are important materials owing to their tremendous applications and useful properties. However magnetic and electrical properties of Cu substituted BaM haven’t been studied yet. In the present study, Cu doped BaM samples having chemical formula BaFe12−xCuxO19 (where x = 0, 0.1, 0.3 and 0.5) were synthesized by conventional solid state mixed oxide route. X-ray diffraction and Fourier transform infrared spectroscopy confirmed the formation of hexagonal magnetoplumbite structure with space group P63/mmc as the major phase in all the samples. Scanning electron microscopy revealed the dense structure of undoped and doped samples with platelet-like morphology. Vibrating sample magnetometry showed a large decrease in the coercivity of BaM without the loss of saturation magnetization by the addition of Cu. Magnetic measurement at cryogenic temperature (25 K) revealed that Cu doped sample showed less variation in magnetic properties on decreasing the temperature as compared to undoped BaM samples. Room temperature dielectric studies showed that addition of Cu caused a decrease in dielectric loss however it increased at higher substitution level i.e. x = 0.5. High temperature conductivity studies revealed that single-ionized oxygen vacancies are responsible for conduction in Cu doped BaM.

Exploring the origins of the Dzyaloshinskii-Moriya interaction in MnSi

By using magnetization and small-angle neutron scattering (SANS) measurements, we have investigated the magnetic behavior of Mn_{1-x}Ir_{x}Si system to explore the effect of increased carrier density and spin-orbit interaction on the magnetic properties of MnSi. We determine estimates of the spin wave stiffness and the Dzyalloshinski-Moria, DM, interaction strength and compare with Mn_{1-x}Co_{x}Si and Mn_{1-x}Fe_{x}Si. Despite the large differences in atomic mass and size of the substituted elements, Mn_{1-x}Co_{x}Si and Mn_{1-x}Ir_{x}Si show nearly identical variations in their magnetic properties with substitution. We find a systematic dependence of the transition temperature, the ordered moment, the helix period and the DM interaction strength with electron count for Mn{1-x}Ir{x}Si, Mn_{1-x}Co_{x}Si, and Mn_{1-x}Fe_{x}Si indicating that the magnetic behavior is primarily dependent upon the additional carrier density rather than on the mass or size of the substituting species. This indicates that the variation in magnetic properties, including the DM interaction strength, are primarily controlled by the electronic structure as Co and Ir are isovalent. Our work suggests that although the rigid band model of electronic structure along with Moira's model of weak itinerant magnetism describe this system surprisingly well, phenomenological models for the DM interaction strength are not adequate to describe this system.

Cation Distribution Assisted Tuning of Magnetization in Nanosized Magnesium Ferrite

The MgFe2O4 nanoparticles are synthesized by combustion method and annealed at different temperatures from 500 to 1000 °C. Magnetic properties, morphology, valence states of iron, crystal structure, and microstructure of the samples are investigated systematically by vibrating sample magnetometer, field emission scanning electron microscope, transmission electron microscopy, X‐ray absorption spectroscopy, and synchrotron X‐ray diffraction. Cation distribution is determined from synchrotron X‐ray diffraction data using Rietveld refinement combined with extended X‐ray absorption fine structure spectroscopy. The results indicates that all the samples are phase‐pure with crystallite size ranging from 11 to 41 nm. By adjusting the annealing temperature, cation distribution and particle size can be changed, and consequently leading to the change in structure and magnetic properties. The saturation magnetization of the samples are enhanced significantly compared to that of the bulk material. The variation of magnetic properties is discussed based on cation distribution, particle size, valence state, surface effect, and spin canting.

Effect of decreasing Mg2+ and Zr4+ substitution on the structural, ferroelectric and magnetic properties of BF-PT solid solutions

Mg2+ and Zr4+ co-substitution in perovskite materials is known to have a pronounced effect on their tetragonal distortion and other physical properties. This study reports the variation in structural, ferroelectric and magnetic properties of (BiMg0.5(1−x)Zr0.5(1−x)FexO3)0.45− (PbTiO3)0.55 solid solutions with x varying from 0.7 to 1.0. The XRD analysis shows an increase in tetragonal distortion from 1.07 to 1.12 with increase in x. The increasing tetragonal distortion has been observed to be directly correlated with the decrease in BO bond length from 1.55 Å to 1.20 Å. The AO bond length remains unchanged. The grain size was observed to decrease slightly with increasing x (up to x = 0.9). The ferroelectric measurements show that remnant polarisation (Pr) decreases from 10.19 μC/cm2 to 0.64 μC/cm2. The magnetic measurements revealed that all the samples exhibit antiferromagnetic behaviour with a maximum Mr value of 11.205* 10−4emu/g for x = 0.9.

Magnetic domains in Tb-Fe-Co thin films under anisotropy tilt

Tailoring of magnetic domains of Tb-Fe-Co thin films with rapid thermal processing has been reported in this paper. While the as-deposited films show elongated, inter-connected domains with high out-of-plane magnetic phase contrast, the rapid thermal processed films at 550 °C with different time intervals display deterioration of magnetic contrast. A longitudinal extension of domains has been observed with the processing time of 5 min. With subsequent increase in processing time, the domain patterns exhibit considerable decrease in magnetic phase difference combined with strong intermixing between two oppositely magnetized areas. The out-of-plane magnetic contrast is seen to be very weak for the Tb-Fe-Co film processed for 30 min. The domain morphology and the contrast variation have been modeled with micromagnetic simulations, considering the in-plane (along xz plane) tilt of anisotropy axis. The ground state energy profile and the variation in magnetic properties indicate the threshold tilt angle to be around 30° wherein the in-plane and out-of-plane squareness ratio and coercivities are comparable and hence the system shows a spin re-orientation behavior at higher tilt angles.

Zn-doped SnO2 nanoparticles: Structural, optical, dielectric and magnetic properties

Zn-doped SnO2 nanoparticles have been synthesized by the chemical precipitation method with the Zn contents ([Formula: see text]) of 1, 2 and 4 wt.%. The nanoparticles are crystalline in all cases, with the average particle size decreasing from 13.4 nm to 7.71 nm as the Zn concentration increases. The visible photoluminescence emission is observed in Zn-doped SnO2 nanoparticles, with larger emission intensity at elevated Zn content. The dielectric constant has a strong doping dependence, which is evidently enhanced with increasing Zn content. Magnetization measurements reveal the enhancement in saturation magnetization and remanence magnetization, while the reduction in coercive field is observed with increasing amount of Zn dopant. The variation of optical, dielectric and magnetic properties is due to the incorporation of Zn in SnO2 with smaller particle size and higher defect density. The present study clearly reveals the doping-induced ferromagnetism in Zn-doped SnO2 nanoparticles, having applications in ultrahigh dielectric materials, high frequency devices and spintronics.

Some Features of the Variation of the Magnetic Field Characteristics in the Umbra of Sunspots During Flares and Coronal Mass Ejections

The observed variations of the magnetic properties of sunspots during eruptive events (solar flares and coronal mass ejections (CMEs)) are discussed. Variations of the magnetic field characteristics in the umbra of the sunspots of active regions (ARs) recorded during eruptive events on August 2, 2011, March 9, 2012, April 11, 2013, January 7, 2014, and June 18, 2015, are studied. The behavior of the maximum of the total field strength Bmax, the minimum inclination angle of the field lines to the radial direction from the center of the Sun αmin (i.e., the inclination angle of the axis of the magnetic tube from the sunspot umbra), and values of these parameters Bmean and αmean mean within the umbra are analyzed. The main results of our investigation are discussed by the example of the event on August 2, 2011, but, in general, the observed features of the variation of magnetic field properties in AR sunspots are similar for all of the considered eruptive events. It is shown that, after the flare onset in six AR sunspots on August 2, 2011, the behavior of the specified magnetic field parameters changes in comparison with that observed before the flare onset.

Interface-engineered oxygen octahedral coupling in manganite heterostructures

Control of the oxygen octahedral coupling (OOC) provides a large degree of freedom to manipulate physical phenomena in complex oxide heterostructures. Recently, local tuning of the tilt angle has been found to control the magnetic anisotropy in ultrathin films of manganites and ruthenates, while symmetry control can manipulate the metal insulator transition in nickelate thin films. The required connectivity of the octahedra across the heterostructure interface enforces a geometric constraint to the 3-dimensional octahedral network in epitaxial films. Such geometric constraint will either change the tilt angle to retain the connectivity of the corner shared oxygen octahedral network or guide the formation of a specific symmetry throughout the epitaxial film. Here, we will discuss the control of OOC in manganite heterostructures by interface-engineering. OOC driven magnetic and transport anisotropies have been realized in LSMO/NGO heterostructures. Competition between the interfacial OOC and the strain further away from the interface leads to a thickness driven sharp transition of the anisotropic properties. Furthermore, octahedral relaxation leading to a change of p-d hybridization driven by interfacial OOC appears to be the strongest factor in thickness related variations of magnetic and transport properties in epitaxial LSMO films on NGO substrates. The results unequivocally link the atomic structure near the interfaces to the macroscopic properties. The strong correlation between a controllable oxygen network and the functionalities will have significant impact on both fundamental research and technological application of correlated perovskite heterostructures. By controlling the interfacial OOC, it is possible to pattern in 3 dimensions the magnetization to achieve non-collinear magnetization in both in-plane and out of plane directions, thus making the heterostructures promising for application in orthogonal spin transfer devices, spin oscillators, and low field sensors.

Single crystal growth and variation of thermodynamic and magnetic properties of Pr1−xLaxAlO3 (x = 0, 0.8)

Two approaches to using optical floating zone (OFZ) technique for single crystal growth of the perovskite Pr1−xLaxAlO3 are discussed, along with the influence on the physical properties of the resulting single crystals due to oxidizing and reducing post anneals. In method one (M1) we used pre-reduced Pr2O3 powder starting material, while in the other method, M2, we employed an argon 5% hydrogen reducing environment during the floating zone single crystal growth. Magnetic susceptibility of the low temperature monoclinic phase of Pr0.2La0.8AlO3 is shown to be sensitive to the precise annealing protocol followed. For the post-growth reduced single crystal the magnetic susceptibility is flat across the R-3c to C2/m structural transition, whereas the oxidized and as-grown samples display a sharp upturn and downturn, respectively. We attribute the low temperature susceptibility differences to relative proportions of Pr3+ and Pr4+.

Microwave-Hydrothermal Synthesis of Y3Fe5O12 Nanoparticles: Sintering Temperature Effect on Structural, Magnetic and Dielectric Properties

Herein, we report a facile microwave-assisted hydrothermal method for the preparation of yttrium iron garnet (YIG, Y3Fe5O12)nanocrystals and realized the synergy between its structural and magnetic properties. The as-prepared powder thermal stability was characterized in detail by using thermogravimetric-differential thermal analysis (TG-DTA). The synthesized powder was microwave sintered at six different temperatures ranging from 973 to 1373 K for 60 min and characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Magnetic properties were investigated by vibrating-sample magnetometer (VSM) and ferromagnetic resonance (FMR) studies. The frequency variation of dielectric and magnetic properties was measured in the frequency range of 100 kHz–1.8 GHz. The observed magnetic and dielectric parameters such as saturation magnetization, coercivity, permeability, linewidth, dielectric constant and magnetodielectric losses are strongly affected by sintering temperature. The saturation magnetization and coercivity of YIG were found in the range 14.4–28.0 emu/g and 35–87 Oe, respectively. Furthermore, the FMR linewidth decreases from 844 to 204 Oe. This analysis undoubtedly demonstrates that the synthesis method and sintering temperature have the prominent effect on the electrical and magnetic properties of YIG and would be very useful for the garnet-based microwave device applications.

Development and application of measurement techniques for evaluating localised magnetic properties in electrical steel

This paper reports the development of a measurement probe which couples local flux density measurements obtained using the needle probe method with the local magnetising field attained via a Hall effect sensor. This determines the variation in magnetic properties including power loss and permeability at increasing distances from the punched edge of 2.4% and 3.2% Si non-oriented electrical steel sample. Improvements in the characterisation of the magnetic properties of electrical steels would aid in optimising the efficiency in the design of electric machines.

Stone-Wales defected molecular-based [formula omitted] nanoribbons: Thermal and magnetic properties

Thermal and magnetic properties of pristine and Stone-Wales (SW) defected zigzag mixed spin-2,5/2AFeIIFeIII(C2O4)3 nanoribbons have been investigated using Monte Carlo simulations. The variation in thermal and magnetic properties has been examined in terms of the number and the positions of SW-defects relative to the edges and the widths of ribbons, as well as to the temperature. Many interesting phenomena have been obtained, such as first and second order phase transitions, N-type compensation behavior and compensation temperature originating mainly from the antiferromagnetic exchange interaction between magnetic ions FeIII and FeII. Furthermore, different hysteresis loop behaviors, such as a single and quintuple hysteresis loops which exhibit different number of steps and various shapes have been observed.

Microwave-assisted synthesis and magnetic properties of M-SrFe12O19 nanoparticles

Strontium hexaferrite nanoparticles were synthesized by a microwave-assisted hydrothermal process. The variation of structure, morphology and magnetic properties of the as-produced particles and after annealing temperatures were carefully analysed. Pure M-SrFe12O19 powders were synthesized at T = 200 °C using a heating rate of 25 °C.min−1. The particles exhibited a magnetic coercivity of 95 kA.m−1 (µ0Hc = 0.12 T), explained by the shape of the particles that crystallized as very thin platelets with a micrometer size diameter and a very high aspect ratio in which a competition between shape and magnetocrystalline anisotropy takes place. The coercivity was strongly enhanced with Hc = 360 kA.m−1 (µ0 Hc = 0.445 T) by annealing at the optimum temperature of 1000 °C. In order to optimize the particle morphology and magnetic properties after annealing, the heating rate of the microwave synthesis was increased. At T = 200 °C using a heating rate of 40 °C.min−1 the particle exhibited a size in the range 20–100 nm. The powder crystallized as a mixture of hexaferrite and ferrihydrite. After annealing at 1000 °C, M-SrFe12O19 with a small amount of hematite (<15%) was obtained. The coercivity was strongly enhanced to reach the value Hc = 465 kA.m−1 (µ0Hc = 0.585 T).

Flooding history of Lake Nakaumi, western Japan, inferred from sediment records spanning the past 700 years

ABSTRACTManagement of flood risk can benefit from a knowledge‐based approach to flooding history. However, the data on such events are often insufficient for an objective evaluation of flooding characteristics such as their intensity. Therefore, we analyzed a 14C‐dated sediment core recovered from near the Iinashi River mouth in Lake Nakaumi, western Japan, and reconstructed flooding records over the past 700 years from rock magnetism, grain‐size distribution and sediment geochemistry. The sediment core contained three black layers, characterized by high magnetic susceptibility, low anhysteretic remanent magnetization to saturation isothermal remanent magnetization ratio, high total organic carbon (TOC) to total nitrogen ratio, and coarse mean grain size, which we identified as possible flooding event deposits. Moreover, the chemical index of alteration was low and the TOC to total sulfur ratio was high in these layers, indicating intensified erosion associated with more freshwater inflow due to the flood events. We tentatively correlated the three event deposits with historical floods along the Iinashi River in AD 1596, 1666 and 1826. The variations in rock magnetic and geochemical properties suggest that the flooding in AD 1666 may have been the least extreme of the events detected in the core.

Magnetic, electrical and dielectric properties of microwave sintered Sr1−x La x Fe12−x Ni x O19 (x = 0−0.35) hexaferrites used for nonreciprocal LTCF devices

The Sr1−x La x Fe12−x Ni x O19 (x = 0−0.35) hexaferrites with 3 wt% Bi2O3 additive were prepared by microwave sintering method at 870 °C. Crystal structure, microstructure, magnetic, electrical, and dielectric properties of these low temperature sintered ferrites were investigated. The results show that the pure M-type phase is obtained for the ferrites with 0≤ x ≤0.25. With further increasing substitution amount, the multiphase structure is inevitably formed, and the LaFeO3 phase coexists with the M-type phase. In single M-type phase region, the variation of magnetic properties with La3+–Ni2+ substitution amount can be well explained based on the occupancy effects of La3+ and Ni2+ in magnetoplumbite structure. Besides, the electrical transport and polarization behaviors of the ferrites are clearly discussed. It suggests that the appropriate La3+–Ni2+ substitution (x = 0.2) improves their intrinsic magnetic and electrical properties for applying in nonreciprocal low temperature co-fired ferrite (LTCF) devices.

Magnetic properties and magnetization reversal mechanism of Nd-Fe-B nanoparticles synthesized by a sol-gel method

Nd–Fe–B oxide powders with various pH were prepared using chloride and nitrate precursors including NdCl3·6H2O, FeCl3·6H2O, H3BO3, Nd2O3, Fe(NO3)3·9H2O, HNO3, citric acid (CA), ethylene glycol (EG) by Pechini type sol–gel method. The pH of chloride and nitrate base sols were 0 and 2.2, respectively. Mixed oxide powders were obtained by calcination and annealing the gels. These oxides by using a reduction-diffusion process under high vacuum and employing CaH2 as reducing agent at 800°C were hated to prepare Nd2Fe14B nanoparticles. The role of pH on phase, morphologies, microstructure, and magnetic properties of the powders were investigated. The results show that with a decrease in pH, the average particle size and coercivity of Nd–Fe–B oxide powders were decreased and increased, respectively. Nd2Fe14B nanoparticles were formed successfully after reduction process. The average particle size of reduction treated products were 30 and 65nm for powders which made of chloride and nitrate base metal salts, respectively. Final powders which made of chloride and nitrate base metal salts had a saturation magnetization of 127.7emu/g and 122.8emu/g while the coercivity of samples were 3.32kOe and 1.82kOe, respectively. The experimental results in the angular dependence of coercivity indicated that the normalized coercivity of the permanent magnets Hc(θ)/Hc(0) obeys the 1/cosθ law and intermediate between the 1/cosθ law and Stoner-Wohlfarth formula for different Nd2Fe14B magnets which made of nitrate and chloride base metal salts, respectively. Also, the results show that different Nd2Fe14B magnets which made of nitrate and chloride base metal salts had the maximum energy product of 5 and 16 MGOe, respectively. The Henkel plot showed that magnetic phases in synthesized NdFeB magnets which made of chloride and nitrate base metal salts were coupled by exchange and dipolar interactions, respectively. Different average particle size, morphology and microstructure were the reasons for variation of magnetic properties.

Magnetic properties and magnetodielectric effect in Y-type hexaferrite Ba0.5Sr1.5Zn2-xMgxFe11AlO22

The effect of Mg substitution on structural, magnetic, and dielectric properties of Y-type hexaferrite Ba0.5Sr1.5Zn2-xMgxFe11AlO22 (x = 0, 0.4, 0.8, 1.2, 1.6, 2.0) prepared by the solid state reaction method was investigated. The X-ray diffraction patterns are analyzed by Rietveld refinement method and the hexagonal structure with R3−m was confirmed. The magnetic transition temperatures associated with the longitudinal conical to proper screw phase transition (T1) and proper screw to ferrimagnetic phase transition (T2) can be modulated by varying Mg content. For x ≤ 1.2 samples, the transition temperature T2 monotonically increases with increasing Mg substitution, suggesting the possibility that the helical spin order of Mg substituted Y-type hexaferrites is sustained up to higher temperatures than that of undoped samples. The saturation magnetization at room temperature increases to a maximum with Mg content x = 1.2 and then decreases with x. The variations of magnetic properties can be attributed to the difference in the preferential site for Zn and Mg and different distribution of Fe3+ ions over tetrahedral and octahedral sites. The results of magnetic field dependence of dielectric constant, i.e., magnetodielectric effect, at various temperatures imply that the doped samples show magnetically induced ferroelectricity up to 250 K. The intrinsic magnetodielectric effect is observed in all the samples. It is worthy to note that the magnetodielectric effect measured below 200 K increases with increasing Mg content, which is probably attributed to the variation of magnetic structures. The Mg-doped hexaferrites Ba0.5Sr1.5Zn2-xMgxFe11AlO22 may be potential candidates for application in magnetoelectric devices.

Erratum to: Variation of structural, optical, dielectric and magnetic properties of SnO2 nanoparticles

Erratum to: Variation of structural, optical, dielectric and magnetic properties of SnO2 nanoparticles

Magnetic evidence of anthropogenic dust deposition in urban soils of Shanghai, China

The magnetic particulates from anthropogenic activities can be detected by magnetic methods rapidly and cost-effectively. This study focused on the investigation of vertical variations in magnetic properties in soil profiles and magnetic enhancement originating in Baoshan, Shanghai. Also the feasibility of using arable and urban park soils as a new context for magnetic monitoring was explored. A combination of magnetic and scanning electron microscopic (SEM) techniques was applied to three soil profiles. Non-pedogenic magnetic enhancement in topsoil was recorded at all three sites accompanied by coarsening of magnetic grain size. The dominant magnetic properties reflect multi-domain (MD) and pseudo-stable single domain (PSD) ferrimagnetic minerals. Both of magnetic concentrations and grain size decrease with the depth, depending on the pollutant input, soil type and degree of vertical mixing. SEM images confirmed the presence of anthropogenic particulates fly-ash. It was concluded from this study that topsoil magnetic enhancement arising from atmospheric contaminants was readily identifiable in both arable fields and urban parks, thus broadening the scope of magnetic research on urban and industrial pollution.