Coercivity Squareness Research Articles

Variation of magnetic properties by heat treatment of dispersed oriented sheets using plate-shaped strontium ferrite particles

Abstract Plate-shaped hexagonal SrFe12O19 particles synthesized using the molten salt method were dispersed in a resin, and oriented sheets were prepared by coating the dispersion onto quartz substrates. The oriented sheets on quartz substrates were heat treated at 300–900 ℃. The variations in the coercive force and squareness of the oriented sheets before and after heat treatment were examined. The coercive force remarkably increased with increasing heat treatment temperature, exhibiting a maximum increase rate of approximately 16 % in the heat treatment at 800 ℃. The increase in coercive force suggests a reduced effect of shape anisotropy due to the stacking of the plate surfaces, caused by the removal of resin between the particles; this highlights the influence of crystalline anisotropy.

The effect of diameter on hysteresis loop squareness in iron nanowires array by micromagnetic simulation

Utilization of micromagnetic simulation is a very attractive subject to understand the magnetic behavior of nanowire arrays that tune their geometrical features and magnetic properties. Here, the micromagnetic simulations utilize to investigation of the single, and a 3 × 3 array of iron nanowires with diameters from 30 to 60 nm. The diameter size and the distance between the wires are selected according to the fabrication of iron nanowires grown in alumina templates. The simulation indicated that an increase in diameter led to a decrease in the coercive field and squareness ratio in both single nanowires and nanowire arrays. Besides, the simulation discloses that the magnetization reversal process of the nanowires with diameters more than 42 nm occurs through the nucleation and propagation of vortex domain walls. In the nanowires array, an increase in wire diameter increases the number of jumps in the hysteresis loop, indicating a more magnetic interaction between the nanowires.

Evaluation of magnetic anisotropy in oriented plate-shaped strontium ferrite particles

Plate-shaped hexagonal SrFe12O19 particles, synthesized using potassium bromide as the molten salt flux, were dispersed in the resin using a planetary ball mill. Oriented sheets were prepared by coating the dispersion onto the films under a magnetic field. The coercive force and squareness ratio of the oriented sheets were 412 kA m−1 and 0.91, respectively. The magnetic anisotropy field was determined by measuring the rotational hysteresis losses of the oriented sheets with a magnetic torque meter. The anisotropy field was distributed in the range of approximately 200–1100 kA m−1, and particles with an anisotropy field of 478 kA m−1 comprised the majority. The magnetic anisotropy energy estimated from the magnetic anisotropy field was 104 KJ m−3. Assuming a reduction in the crystalline anisotropy field along the c-axis due to simply the shape anisotropy field resulting from the platelet shape of the particles, particles occupying the majority exhibited a maximum anisotropy field of 823 kA m−1.

Combination strategy for high-performance Sm(CoFeCuZr)z sintered permanent magnet: Synergistic improvement of the preparation process

In this paper, a new pulverizing approach consisting of strip-casting, hydrogen decrepitation, and jet milling was adopted to produce Sm(Co0.65Fe0.28Cu0.05Zr0.02)7.6 sintered magnet with excellent magnetic performance. By slowing down the rotating speed of the wheel roller during strip-casting, the proportion of the monocrystalline particles is increased, thus the degree of orientation is increased and thereby the remanence is raised. The hydrogen decrepitation and jet milling processes show high pulverizing efficiency, and give to a magnetic powder with uniform composition and concentrated particle size distribution. After the hydrogen absorption process, the presence of residual hydrogen can accelerate the sintering process, promotes grain growth, and ultimately enhances the coercivity and demagnetization curve squareness. The advantages of the combined approach were further explored by optimizing the solid-solution treatment, which can help to form a clear and complete cellular structure, increase the Cu concentration difference between the cell phase and cell boundary phase, and significantly lower the volume fraction of the 2:17R' intermediate phase. Promising magnetic properties are achieved eventually with Br=11.78 kG, Hcj=17.67 kOe, Sr=92.2%, and (BH)max=31.98 MGOe.

Tb–Cu grain boundary diffusion effects on single- and multi-main-phase Nd–Fe–B based magnets

Although Tb diffusion is deeper in multi-main-phase (MMP) magnets than in single-main-phase (SMP) magnets, the coercivity enhancement and squareness of diffused MMP magnets are lower than those of SMP magnets due to the larger gradient of anisotropy.

Study of ferromagnetic and ferroelectric properties of nanocrystalline Bi2Mn4O10

Nano-crystalline bismuth manganese oxide Bi2Mn4O10 was prepared from Bi2O3 and MnO2 by mechanochemical technique at different milling times followed by heat treatment at 1073 K. The crystal structural were obtained using X-ray diffraction (XRD) and TEM. We obtained the variation of the crystallite size and micro-strain with milling time. The magnetic parameters include the saturation magnetization, coercivity and squareness ratio were obtained by vibrating sample magnetometer (VSM). Each of the coercive field, Squareness ratio and saturation magnetization increased with increasing the milling time. The electrical conduction of the prepared samples was evaluated by AC conductivity measurements at different temperature, the dielectric parameters were plotted against temperature at different frequencies. The conduction mechanism is described by the correlated barrier hopping model (CBH). The recoverable energy density and loss energy was obtained to calculate the storage energy efficiency.

Optimization, structural, optical and magnetic properties of TiO2/CoFe2O4 nanocomposites

Magneto-optical TiO2/xCoFe2O4 nanocomposites having various concentrations of CoFe2O4 (x = 2, 4 and 6 wt %) were prepared using facile mechanical mixing. X-ray diffraction was employed for the phase examination and microstructure parameters. X-ray diffraction spectra proved the formation of two separate phases: tetragonal titanium dioxide (TiO2) and face-centered cubic cobalt iron oxide. The structure was further verified by recognizing the selected area electron diffraction (SAED) pattern recorded by a high-resolution transmission microscope. The optical investigation of the prepared nanocomposites verified that the optical band gap values varied from 3.1 eV for pure TiO2 to 3.05 eV for TiO2/CoFe2O4 (6 wt %). The refractive index, optical dielectric constant and loss factor were discussed in detail. The nanocomposites (TiO2/xCoFe2O4) demonstrated ferromagnetic characteristics and their magnetic parameters were affected by the CoFe2O4 percentage in the composites. The sample x = 2 wt % depicted the maximum magnetic exchange bias at room temperature. Moreover, it showed maximum coercivity (HC) and magnetic squareness ratio (SQ), which makes it suitable for spintronic applications.

Electrochemical Deposition of Fe–Co–Ni Samples with Different Co Contents and Characterization of Their Microstructural and Magnetic Properties

In this study, to explore the effect of Co contents on the electroplated Fe–Co–Ni samples, three different Fe–Co33–Ni62, Fe–Co43–Ni53, and Fe–Co61–Ni36 samples were electrochemically grown from Plating Solutions (PSs) containing different amounts of Co ions on indium tin oxide substrates. Compositional analysis showed that an increase in the Co ion concentration in the PS gives rise to an increment in the weight fraction of Co in the sample. In all samples, the co–deposition characteristic was described as anomalous. The samples exhibited a predominant reflection from the (111) plane of the face–centered cubic structure. However, the Fe–Co61–Ni36 sample also had a weak reflection from the (100) plane of the hexagonal close–packed structure of Co. An enhancement in the Co contents caused a strong decrement in the crystallinity, resulting in a decrease in the size of the crystallites. The Fe–Co33–Ni62 sample exhibited a more compact surface structure comprising only cauliflower–like agglomerates, while the Fe–Co43–Ni53 and Fe–Co61–Ni36 samples had a surface structure consisting of both pyramidal particles and cauliflower–like agglomerates. The results also revealed that different Co contents play an important role in the surface roughness parameters. From the magnetic analysis of the samples, it was understood that the Fe–Co61–Ni36 sample has a higher coercive field and magnetic squareness ratio than the Fe–Co43–Ni53 and Fe–Co33–Ni62 samples. The differences observed in the magnetic characteristics of the samples were attributed to the changes revealed in their phase structure and surface roughness parameters. The obtained results are the basis for the fabrication of future magnetic devices.

The ferroelectric response of island-like regions in bismuth ferrite oxide compound

We investigate the piezoelectric and ferroelectric properties in island-like ferroelectric regions of bismuth ferrite oxide films. Samples were synthesized by the simultaneous laser ablation of bismuth, and iron oxide targets. Bismuth content in the deposited films was controlled with the plasma density (Np) that is produced during the ablation of the Bi target. A change in the NpBi alters the Bi incorporation into the films. Relatively homogeneous films deposited at NpBi of 11 × 1012 cm−3 with an effective piezoelectric coefficient (deff) of ~15 pm/V served as the starting point. A reduction of NpBi at 2 × 1012 cm−3 produced films with almost null piezoelectrical response but at 4 × 1012 cm−3 caused the formation of island-like ferroelectric regions with large deff values that spans from 70 to 108 pm/V. The island-like regions presented upright hysteretic phase-switching loops with low coercive voltages and squareness values close to unity. The resulting large deff values were attributed to the reduction of the substrate-clamping effect, the (001)-textured BiFeO3 structure, and the coexistence of secondary phases with the main BiFeO3 phase. The mechanisms for polarization switching and the electromechanical response of the island-like regions are discussed. Finally, some preliminary results of ferroelectric fatigue experiments in island-like regions are presented.

Facile sol-gel method derived Au nanoparticles decoration nickel ferrites thin films: Effect on optical and magnetic properties

Noble metal Au nanoparticles (Au NPs) decoration nickel ferrite (hereafter abbreviated as NFA-x, x = 0, 0.04, 0.08 and 0.12) thin films were synthesized on quartz and Pt/Ti/SiO2/Si substrates by a facile sol-gel method. The structural, optical and magnetic performances of NFA-x thin films have been investigated. The XRD patterns revealed the formation of cubic spinel ferrite structure. The SEM analysis indicated that NFA-x thin films were dense and uniform, which also confirm that crystalline size decreased with increasing of Au content. A remarkable surface plasmon resonance (SPR) features has been observed in NFA-0.12 films. The optical band gap of NFA-x thin films decreased with increasing Au concentration. In addition, our results revealed that the magnetism was highly depending on the Au concentration. The saturation magnetization remarkable decreased then sharply increased with increasing of Au content, which is attributed to Au NPs decoration effect. However, the coercive field and squareness ration showed increasing trend with increasing of Au concentration. Our work suggests that Au nanoparticles decoration nickel ferrites thin films have promising applications in multifunctional materials field.

Enhanced magnetic properties of magneto-electrodeposited Co and Ni nanowires

The present paper examines the influence of an applied magnetic field B (AMF B) on the physical and chemical properties of electrodeposited Cobalt (Co) and Nickel (Ni) nanowires into anodic aluminum oxide (AAO) membranes. The deposition potential and the effect of the AMF B on the mass transport rate of Ni and Co ions to the bottom of the pores were examined using cyclic voltammetry (CV) and current density–time curves. X-ray diffraction (XRD) studies show that the AMF B promotes the growth of Co and Ni into the membrane pores. The AMF B effect on the morphology and chemical composition of the electrodeposited nanowires were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS), respectively. Co nanowires exhibit a high coercive field Hc, shape anisotropy, and squareness ratio MMs than those corresponding to Ni nanowires.

Cr3+-doped nanocrystalline nickel–magnesium–cobalt spinel ferrite: microstructural and magnetic

A series of chemical sample with formulae Ni0.2Mg0.2Co0.6Fe2−xCrxO4 (0.00 ≤ x ≤ 0.1; step 0.025) were prepared by sol–gel automatic combustion at 950 °C. X-ray diffraction analysis found that the sample has characteristic peaks belonging to spinel, and Fourier transform infrared (FTIR) analysis found that the sample has a characteristic absorption band indicating the structure of spinel. This above findings can confirm that all samples belong to the single-phase cubic spinel structure. The average crystallite size and the lattice constant increase first and then decrease with the increase of Cr3+ ion content. Surface morphology analysis observed that the shape of the ferrite sample was spherical nanoparticles. The surface morphology of the sample and the stoichiometric ratio of each element contained in it are analyzed by energy-dispersive spectrometer. The sample was subjected to an external magnetic field of 15 KOe at room temperature, and a vibrating sample magnetometer was used to measure the magnetic properties of Ni0.2Mg0.2Co0.6Fe2−xCrxO4 nano-ferrite. Compared with other samples doped Cr3+ ion, the magnetic properties of the sample reach to best when the doping content is x = 0.025, and the Ms, Mr and S* (coercivity squareness) also reach the maximum at the same time.

THE ROLE OF DEPOSITION TEMPERATURE ON PARTICLE SIZE, ROUGHNESS PARAMETERS, MAGNETIC AND STRUCTURAL FEATURES OF ELECTROCHEMICALLY GROWN Ni–Fe/ITO SAMPLES

In this work, the impact of the deposition temperature (DT) on the particle size, roughness parameters, coercive force, squareness and structural features of the Ni–Fe samples electrochemically deposited onto glasses covered with indium tin oxide (ITO) was researched. An increase in the DT from 20 to 40 °C led to a very slight increase in the Fe concentration of the samples, revealing that the effect of the DT on the chemical composition was insignificant. The crystal structure was a face–centered cubic (fcc) and the preferred growth orientation was in the [111] direction irrespective of the DT. The crystallization of the samples improved, the size of the crystallites increased and the strength of the [111] growth orientation diminished with the DT. An increment in the DT resulted in a strong enhancement in the particle size and surface roughness. Further surface analysis indicated that the sample surface had a well spread out height distribution at the DT of 40 °C, while the sample surfaces at lower DTs 20 and 30 °C had narrow height distributions. In addition to that, the peaks were found to be predominant on the sample surfaces at lower DTs (20 and 30 °C), whereas the deep valleys were predominant on the sample surface at the DT of 40 °C. Magnetic measurements confirmed the existence of a semi–hard magnetic property in all samples. Compared to other samples produced at lower DTs (20 and 30 °C), the Ni–Fe sample electroplated at the DT of 40 °C possessed the highest coercive force and squareness values. Moreover, the magnetic characteristics of the samples were compatible with their morphological and structural characteristics.

THE ROLE OF DEPOSITION TEMPERATURE ON PARTICLE SIZE, ROUGHNESS PARAMETERS, MAGNETIC AND STRUCTURAL FEATURES OF ELECTROCHEMICALLY GROWN Ni–Fe/ITO SAMPLES

In this work, the impact of the deposition temperature (DT) on the particle size, roughness parameters, coercive force, squareness and structural features of the Ni–Fe samples electrochemically deposited onto glasses covered with indium tin oxide (ITO) was researched. An increase in the DT from 20 to 40 °C led to a very slight increase in the Fe concentration of the samples, revealing that the effect of the DT on the chemical composition was insignificant. The crystal structure was a face–centered cubic (fcc) and the preferred growth orientation was in the [111] direction irrespective of the DT. The crystallization of the samples improved, the size of the crystallites increased and the strength of the [111] growth orientation diminished with the DT. An increment in the DT resulted in a strong enhancement in the particle size and surface roughness. Further surface analysis indicated that the sample surface had a well spread out height distribution at the DT of 40 °C, while the sample surfaces at lower DTs 20 and 30 °C had narrow height distributions. In addition to that, the peaks were found to be predominant on the sample surfaces at lower DTs (20 and 30 °C), whereas the deep valleys were predominant on the sample surface at the DT of 40 °C. Magnetic measurements confirmed the existence of a semi–hard magnetic property in all samples. Compared to other samples produced at lower DTs (20 and 30 °C), the Ni–Fe sample electroplated at the DT of 40 °C possessed the highest coercive force and squareness values. Moreover, the magnetic characteristics of the samples were compatible with their morphological and structural characteristics.

Controllable fabrication and magnetic properties of Nd/Co core/shell nanowires

Ordered Nd/Co100 and Nd/Co200 core/shell nanowire arrays with lengths of ~ 10 μm and diameters of 100 nm and 200 nm were fabricated by two-step electrodeposition into anodic alumina oxide templates. Co-hcp phases were observed in the Nd/Co100 and Nd/Co200 nanowires. Hysteresis curves obtained from the Nd/Co100 and Nd/Co200 nanowires showed that the squareness ratio of the parallel nanowire long axis was greater than that of the perpendicular nanowire long axis. The magnetic properties indicated that the easy axis was parallel to the long axis. The coercivity and parallel squareness ratio in the Nd/Co200 nanowires were greater than those in the Nd/Co100 nanowires, which demonstrated that the Nd/Co200 nanowires exhibited hard magnetism behavior.

Role of nanoscale interfacial defects on magnetic properties of the 2:17-type Sm–Co permanent magnets

Development of miniaturized magnet-associated devices operated at elevated temperatures requires that the 2:17-type Sm(Co, M)z (M = Fe, Cu, Zr) permanent magnets have large magnetic energy product and high coercivity. Raising iron content is essential to enlarge the energy product, however it leads to serious deterioration in coercivity (Hcj) and squareness factor (SF). In order to uncover the underlying microstructural origins, here we performed a comparative study between two nanocell structured Sm(Co0.68Fe0.22Cu0.07Zr0.03)7.5 magnets with different magnetic properties. We found that the nanoscale interfacial defects, including the retained phase at the grain edges and the intermediate rhombohedral phase (2:17R’) at the cell edges, act as extra defects that are detrimental to the coercivity as well as the squareness, besides the formerly-reported incomplete cell walls and discontinuous platelets. These microstructural defects build up inhomogeneous pinning sites, at the interfaces between the cell walls and the cell interiors, and at the intersections of the cell walls and the Zr-rich platelets. The comparative results show that the magnet with Hcj = 34.39 kOe and SF = 62.08% contains much less microstructural defects than the one with Hcj = 24.42 kOe and SF = 47.08%. Our work highlights the importance of reducing microstructural defects for achieving high coercivity and large squareness in the iron-rich Sm(Co, M)z permanent magnets.

Comparison of microstructures and magnetic properties in FePt alloy films deposited by direct current magnetron sputtering and high power impulse magnetron sputtering

Single-layered FePt films of 30 nm thickness with random orientation are produced by direct current magnetron sputtering (DCMS) deposited directly onto Corning 1737 glass substrates and then post-annealed at 700 °C for 30 min. In films produced by high power impulse magnetron sputtering (HiPIMS) however, a strong (001) texture of L10 FePt film with isolated island structure is achieved and presents high perpendicular magnetic anisotropy after post-annealing under the same conditions. This is due to the compressive stress in as-deposited FePt films being enhanced greatly by HiPIMS. The films achieved by HiPIMS possess perpendicular coercivity, saturation magnetization and perpendicular squareness of 14.2 kOe, 620 emu/cm3 and 0.98, respectively, which reveal HiPIMS as a good technique to produce single-layered FePt films with high perpendicular magnetic properties.

Perforated alumina templates as a tool for engineering of CoPd film magnetic properties

Abstract The patterning of the CoPd films was performed by the deposition of the Co/Pd multilayers on the nanoperforated templates of anodic aluminum oxide (AAO). We observed that the morphology of aluminum oxide is represented by the hexagonal packed hemispherical wells with a pore in the middle. The morphology of the patterned films follows the features of the initial templates; the magnetic material is deposited mainly in the regions between the pores and on their perimeter. The Co atoms diffuse into the Pd layer already during the film deposition, and discontinuous interfaces of Co and Pd are formed leading to the creation of the CoPd solid solution. The out-of-plane hysteresis loops of the nanoporous films exhibited high values of the coercive field (HC = 2.0–3.6 kOe) and squareness ratio (Mr/MS = 0.7–0.8). This indicates that the nanoporous films retain the perpendicular magnetic anisotropy observed for continuous film. Deteriorated values of effective anisotropy constant Keff for the porous films with respect to the continuous film are explained by the complex morphology of the nanoporous films, which leads to partial deviation of magnetic moments from the direction normal to the sample plane. On the other hand the increase of the values of the coercive field HC of the nanoporous films in comparison to the continuous films is related to the pinning of the magnetic moments on the nanopores. We observed the transition of the magnetization reversal mechanism from the domain wall motion observed for the continuous film, to coherent rotation mode for the nanoporous films. We show that this approach allows us to tune the coercive field HC and the effective magnetic anisotropy constant Keff of the CoPd film by engineering the pore size of the templates.

The effect of affect primes' visibility on effort-related cardiovascular response is moderated by gender

Crystallographically c-axis textured Zn2W barium ferrites (i.e., BaMe2Fe16O27), synthesized by traditional ceramic methods, are presented as a high-magnetic-remanence material for self-biased microwave and millimeter wave applications. A magnetic field orientation process was applied to obtain c-axis texture of ferrite materials while sintering parameters were systematically optimized to obtain high-performance materials for self-biased circulators and isolators. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to confirm structure, crystal orientation, and microstructural morphology of the Zn2W ferrite final product. Room temperature vibrating-sample magnetometry (VSM) was applied to measure hysteresis (M vs. H) loops that provided an evaluation of coercivity (Hc), magnetization (M), and magnetic remanence (Mr) and squareness ratio (Mr/Ms). The ferrite samples sintered at 1020 °C demonstrated excellent magnetic properties, such as high squareness ratio (∼0.8), relative density (89% of theoretical), 4πMS ∼ 3115 Gauss, and coercive fields of ∼1011 Oe.

Ising-tipi çok segmentli nanoyapıda kompozisyon ve sıcaklık bağımlılıkları

In the present study , an Ising-type multisegment nanowire (IMN) with ferromagnetic / non-magnetic segment structure is investigated by means of the effective-field theory (EFT) with correlations. The effects of the composition (p) and temperature (T) on the magnetic hysteresis properties are investigated in detail. The coercive field (H C ) and squareness ( M r /M S ) of the IMN is also derived from hysteresis loops as a function of p and T. In this system, it was found that the p and T have a significant effect on the magnetic behavior. When the obtained theoretical results compare with some experimental works of nanowire in view of hysteresis behaviors, a very good agreement between them is observed.