Remanence Values Research Articles

Rock magnetic properties of Grand Lake sediments as evidence of environmental changes during the last 60 000 years in North‐East Russia

Dansgaard–Oeschger events of the last glacial cycle are widely observed in the North Atlantic sector. In far northeast Asia, however, a lack of data means the presence or absence of these events is uncertain and, if present, the mechanisms that connect this region with the North Atlantic remain unresolved. A sediment record from Grand Lake, North‐East Russia (latitude 60°44′N, longitude 151°53′E), spans much of the last glacial cycle and shows strong variations in magnetic parameters. These variations are related to sedimentation changes that were likely influenced by the palaeoclimate. Rock magnetic properties of a 1020‐cm‐long sediment core were determined for four lithological units. Additionally, samples taken from across the modern catchment aided the interpretation of the magnetic properties of the down‐core sediments. Magnetic minerals in all sediment units consist of detrital, oxidized Ti‐poor titanomagnetites. Sediments of Holocene age (Unit 1) display the lowest values of magnetic susceptibility (MS), saturation magnetization (Js) and saturation remanence (Jrs), and reflect dilution by biogenic silica and organic matter. Variations of magnetic properties in Units 2, 3 and 4, which correspond to Marine Isotope Stages (MIS) 2, 3 and 4, respectively, parallel granulometric changes. Massive sediment structure, which characterizes Unit 3, has a coarser grain size and higher MS, Jrs and Js as compared with the laminated sediments of Unit 2 and Unit 4, suggesting higher‐energy catchment processes. Nine distinct peaks in MS, Js and Jrs within MIS 3 coincide with TiO2 minima and with high pollen percentages of trees and shrubs, supporting the conclusion that lake and catchment sediment processes are associated with fluctuating regional climate. While the dating is not resolved enough to be certain, the data are suggestive that these cycles correlate with Dansgaard–Oeschger events.

Structural Elucidation and Magnetic Behavior Evaluation of Nd-doped Nickel-Cobalt Spinel Ferrites

Nano ferrites crystals of Ni0.4Co0.6NdxFe2-xO4 for 0.00 ? x ? 0.08 with step size of 0.02 were synthesized by sol gel technique with annealing at 950 oC for 6 hours. Spinel phase along with a secondary phase for Nd concentration x ? 0.04 due to formation of NdFeO3 was observed in XRD patterns. Lattice constant and grain size were found in decreasing trend with increasing concentration of Nd as compared to that of undoped nickel cobalt ferrites. X-ray density and porosity both were increased with increasing concentration of neodymium. Two characteristics frequency bands were observed in the range of 400cm-1 to 550 cm-1 which showed successful formation of spinel structure. It is also the evidence of metal-oxygen bonding at octahedral and tetrahedral sites in spinel ferrites. Also, bands for carbon-hydrogen, carboxyl group, carbon-oxygen stretching and iron-cobalt alloys were observed in the FTIR spectra. By using these values of characteristics frequencies, octahedral and tetrahedral radii were calculated and found in decreasing trend with increasing concentration. Force constants are increasing with increase in neodymium concentration. Saturation magnetization, coercivity and remanence values were calculated from the M-H loops. Saturation magnetization showed the decreasing behavior with increase in neodymium concentration. Coercivity showed increasing values as compared to the base sample and also showing reciprocal relation with saturation magnetization. Magnetic moment is decreasing with increase in neodymium concentration.

High magnetic coercive field in Ca‐Al‐Cr substituted strontium hexaferrite

The structural and magnetic properties of Sr0.67Ca0.33Fe9Al3−xCrxO19 submicrometric powders with substitution levels ranging from x = 0 up to x = 3, prepared by sol-gel synthesis method, have been investigated. The powders were characterized by high resolution synchrotron X-ray diffraction, scanning electron microscopy, powder neutron diffraction and MPMS-SQUID magnetometer. The structural analysis shows that upon Ca-substitution of SrFe12O19 at the Sr site and Al–Cr at the Fe sites, the magnetoplumbite structure is preserved, even for large levels of substitutions. The X-ray powder diffraction peak broadening and Williamson-Hall plots analyses indicate an increase of crystallites size and relaxation of the microstrain with increasing amounts of Chromium. The magnetic hysteresis loops reveal high coercivity fields at room temperature, with the highest value of HC = 1125 kA/m (1.41 T) obtained for Sr0.67Ca0.33Fe9Al2.5Cr0.5O19 powder interesting to develop free-Rare Earth high coercivity magnets. The saturation magnetization and remanence values increase monotonically with increasing Cr content while the switching field decreases. The structural Rietveld refinement of combined X-ray/neutron diffraction data shows the affinity of Al3+ and Cr3+ cations to migrate mainly towards (2a) Fe-Oh2 and (12k) Fe-Oh3 sites and only minor amounts is found on the (4f1) Fe-Oh1 octahedral sites. The structural observations corroborate the magnetic properties, demonstrating a correlation between the structure and magnetic properties in Ca–Al–Cr substituted strontium hexaferrite. The role of the particle size to maximize the coercivity properties is discussed.

Thickness induced magnetic anisotropic properties of Tb-Fe-Co thin films

The influence of Tb25Fe61Co14 thin film thicknesses varying from 2 to 300 nm on the structural and magnetic properties has been systematically investigated by using of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, magnetization, and magneto-optic Kerr effect microscopy measurements. Thin film growth mechanism is pursued and controlled by ex-situ X-ray refractometry measurements. X-ray diffraction studies reveal that the Tb25Fe61Co14 films are amorphous regardless of thin films thicknesses. The magnetic properties are found to be strongly related to thickness and preferred orientation. With an increase in film thickness, the easy axis of magnetization is reversed from in-plane to out-of-plane direction. The change in the easy axes direction also affects the remanence, coercivity and magnetic anisotropy values. The cause for the magnetic anisotropy direction change from in-plane to out-of-plane can be related to the preferred orientation of the thin film which depends on the large out-of-plane coercivity and plays an important role in deciding the easy axes direction of the films. According to our results, up to the 100 nm in-plane direction is dominated over the whole system under major Fe-Fe interaction region, after that point, the magnetic anisotropy direction change to the out-of-plane under major Tb-Fe/Tb-Co interaction region and preferred orientation dependent perpendicular magnetic anisotropic properties become more dominated with 2.7 kOe high coercive field values.

Initial Study of Magnetic Characterization of Barium Hexaferrite with the Addition of Cobalt Oxide Prepared by Powder Metallurgy Process

Co3O4 powder was added to barium hexaferrite by powder metallurgy process to determine its effect on the magnetic properties. The variation of the addition of Co3O4 are 0.0, 0.5, 1.0, 2.0, 3.0, and 5.0 wt%. Characterization and magnetic testing included density calculation, Permagraph test, and XRD were performed in order to elucidate the effect of Co3O4 addition to its structure and magnetic properties of barium hexaferrite. The magnetic density obtained was in the ranges of 3.2 - 4.35 g/cm3. From the permagraph test, it is found that the value of remanence (Br) was in between 1.18 and 1.5 kG. The value of coercivity (Hc) was in the range of 0.594 - 3.366 kOe, and the maximum product energy (BHmax) was found to be in between 0.07 and 0.48 MGOe. From the XRD analysis, it was found that two types of barium hexaferrite were formed, namely barium hexaferrite type M(BaFe12O19) and X(Ba2Fe30O46). It is concluded that the addition of the Co3O4 compound increased the value of magnetic density and decreased magnetic properties.

Post-Annealing Influence on Magnetic Properties of Rapidly Quenched Ni–Mn–Ga Glass-Coated Microwires

In this article, we showed how the post-annealing process affects the magnetic properties of rapidly quenched Ni-Mn-Ga glass-coated microwires. Microwires with Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">63</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">25</sub> chemical composition, total diameter D = 54.6 μm and metallic nucleus diameter d = 26.7 μm, were prepared by the Taylor-Ulitovsky technique. The annealing temperature was fixed at 873 K, and the time was 1 and 10 h. The microwires were slowly cooled to room temperature after annealing. Based on thermomagnetic curves and hysteresis loops, we suggest crystallographic texture in the wires that considerably affect magnetic properties. The wires' internal structure indicates nanocrystalline state with radial micrometers and submicrometer grains distribution in the wire annealed during 10 h. A ferromagnetic-to-paramagnetic phase transition occurs around room temperature. No signs of a martensitic transformation were found. The difference in magnetization saturation, remanence, and Curie temperature values for 1- and 10-h annealed microwires indicates the influence of internal stresses and that created by the presence of a glass coating.

Magnetic and Mössbauer Effect Study of Ca-Sc Co-doped M-Type Strontium Hexaferrite

The present study investigates the influence of Ca2+-Sc3+ co-dpoing on the magnetic properties of Sr1-x/12Cax/12Fe12-xScxO19 (x = 0.0 to 2.0) hexaferrites. The samples were prepared via a facile autocombustion technique followed by sintering in ambient air. X-ray powder diffraction patterns show the formation of the pure phase of M-type hexaferrite. The lattice parameters a and c increased with the Ca2+-Sc3+ doping. The compounds’ magnetic properties were assessed as a function of temperature (10–300 K) and field (up to 6T). A rapid decline in room temperature coercivity from 5458 to 373 Oe and remanence value from 37 to 13 emu/g and a moderate decline in saturation magnetization from 76.9 to 57 emu/g were observed with increasing doping content from x = 0.0 to 2.0. The phase transition temperature, corresponding to ferrimagnetic to conical, was observed below 100 K, which disappeared at low doping content. The temperature-dependent behavior of magnetization and coercivity is discussed in view of spin non-collinearity due to the change in magnetic anisotropy. The Curie temperature dropped from 769 K at x = 0 to 568 K at the maximum substitution of x=2.0. The room temperature Mossbauer spectral analysis confirmed the preferred occupancy of Sc3+ at the 4f2 site and the influence of Ca2+ on the isomer shift values of the 2b site. The increased quadrupole shift values with the substitution implied distortion in 2b bipyramidal symmetry. The observed changes in magnetic properties and hyperfine parameters are ultimately tied to the preferred occupancy of Sc3+ at the spin-down 4f2 site.

Synthesis and characterizations of magnetically inductive Mn–Zn spinel ferrite nanoparticles for hyperthermia applications

Monodispersed Mn0.5Zn0.5Fe2O4 (~ 14 nm) nanoparticles were prepared by using a chemical co-precipitation technique. The direct mixing method has been used to prepare ferrofluid (base fluid-water) and to investigate their properties for the application of magnetic hyperthermia. Phase identification, crystal structure, and average crystallite size of the prepared samples were revealed in the XRD analysis. It confirms the Fd3m space group cubic spinel structure and average crystallite size ~ 14 nm. From TEM evaluation, the average particle size was found at ~ 16 nm. The 41.12 emu/g magnetization value of the Manganese Zinc Ferrite (MZF) nanoparticles (NPs) was found at room temperature. A negligible coercivity and remanence values confirm the superparamagnetic behavior of MZF nanoparticles at room temperature were confirmed by vibrating sample magnetometer (VSM) analysis. The induction heating analysis on water dispersed MZF Magnetic NPs at 4 kA/m AC magnetic field amplitude and 280 kHz frequency was conducted to use them in the application of hyperthermia. The result specifies that the heating potential of prepared ferrofluids can be reached within 65 s of hyperthermia temperature (42 °C) at lower 4 mg/mL content, indicating that the prepared material can be used as a heating agent for the treatment of magnetic hyperthermia. The specific absorption rate (SAR) was found to be 110.90 W/g. Thus, the obtained results suggest that the prepared MZF nanoparticles are a promising candidate for hyperthermia therapy due to their high heat-generating ability with less time at a lower concentration.

Modification of selective electrode based on magnetic molecularly imprinted polymer for bisphenol A determination

Selective electrodes were modified by using the magnetic molecularly imprinted polymer (MMIP) technique on a screen-printed electrode (SPE) to detect bisphenol A (BPA). Superparamagnetic iron oxide nanoparticles (SPIONs) greatly enhance electrochemical signals due to their superparamagnetic properties. The SPIONs are non-toxic, biocompatible and highly stable. The SPIONs, especially magnetite (Fe3O4), were synthesized from ferrous chloride and ferric chloride using a chemical co-precipitation method. The crystalline structure of the synthesized SPIONs was obtained by X-ray diffractometer, representing cubic inverse spinel structure like magnetite. The synthesized SPIONs had particle sizes of 9.87 ± 2.67 nm, which was confirmed by transmission electron microscope. The magnetic property was measured by a vibrating sample magnetometer, which presented the saturated magnetization, magnetic remanence value and coercivity as 48.76 emu g−1, 0.497 emu g−1 and 6.265 Oe, respectively. The surfaces of modified electrodes were characterized by a scanning electron microscope, which revealed BPA template cavities on the electrode surface. The electrochemical properties were studied by cyclic voltammetry and amperometry. The bisphenol A-magnetic molecularly imprinted polymer electrode (BPA-MMIP/SPE) has a sensitivity of 2.909 with a limit of detection of 2.053 × 10−8 M. The concentration range for BPA detection is 2.5 × 10−8 to 1.00 × 10−4 M, which can be applied to detection in a real sample.

Electrical and magnetic properties of BiFeO3 nanoparticles substituted with high concentrations of cobalt

The 10% and 20% Co-substituted BiFeO3 (BFO) samples were prepared by co-precipitation method. The microstructure, phases formed, electrical and magnetic properties were investigated. The cobalt-substituted BiFe1−xO3 (where x = 0.0, 0.1, and 0.2) showed formation of BiFeO3 (BFO), Bi25FeO40, CoFeO4, and Bi2Fe4O9 phases. The lattice parameter value “a” decreased and “c” increased for BFO as a result of Co substitution, thereby increasing lattice cell volume. The surface morphology and grain shape and size were studied by scanning electron microscope. Enhanced dielectric properties are studied for the Co-substituted BFO nanoparticles. At low frequency, BFO showed dielectric constant value of 40 which increased to 52 and 402 for 10% and 20% Co-substituted BFO samples, respectively. The electrical conductivity in the temperature range 300–700 °C showed semiconducting behavior. Remanence (Mr), saturation magnetization (Ms), and coercivity (Hc) values for BFO are 0.123 emu/g, 6.178 emu/g, and 108.59 G, respectively. The Ms, Mr, and Hc values for 10% cobalt and 20% Co-substituted BFO are 5.742 emu/g, 0.213 emu/g, and 124.86 G and 42.777 emu/g, 24.255 emu/g, and 4127.55 G, respectively. It is concluded that synthesis of pure BiFeO3 is not possible and increase in magnetic parameters are due to the formation of cobalt ferrite.

Characterization and synthesis of Fe3O4@C nanoparticles by in-situ solid-phase method

Fe3O4@C nanoparticles were successfully synthesized by an in situ solid-phase method using FeSO4, FeS2, and PVP K30 as the starting materials under the nitrogen atmosphere. In addition, the mechanism of the synthetic of Fe3O4@C nanoparticles was studied through in situ characterizations. The results showed that the pyrolysis of PVP K30 participated in the solid-phase reaction and resulted in the formation of carbon shells and a reduction in particle size. The structure of the Fe3O4@C nanoparticles was core–shell with the average particle size of ∼30 nm and the thickness of the carbon shell of ∼2 nm. Besides, the Raman spectrum revealed that the carbon shell mostly existed in the form of amorphous carbon. The surface area and the pore volume of the Fe3O4@C nanoparticles were estimated to be 37.74 m2 g−1 and 0.227 cm3 g−1. Magnetization hysteresis curve exhibited the values of coercivity and remanence and saturation magnetization are found to be approximately 0.16 kOe, 12.8 emu g−1, and 77 emu g−1, respectively.

Improved photocatalytic degradation of rhodamine B under visible light and magnetic properties using microwave combustion grown Ni doped copper ferrite spinel nanoparticles

Nanoparticles (NPs) of Cu1-xNixFe2O4 (0 ≤ x ≤ 0.5) have been facilely prepared via combustion through microwave technique. X-ray diffraction outcomes confirmed single-cubic phase synthesis of titled material and mean crystallites size and lattice constants were calculated in range of 19.37–22.69 nm and 8.319–8.248 Å, respectively. The XPS study confirms the chemical elements and oxidations states of Cu0.6Ni0.4Fe2O4 NPs. The high-resolutionSEM study reveals spherical NPs with agglomeration and composition of elements in Cu1-xNixFe2O4 (0 ≤ x ≤ 0.5) was confirmed through EDX study. The Kubelka-Munk model was employed to determine the energy gap of Cu1-xNixFe2O4 NPs and noticed to vary from 2.30 to 2.06 eV. Photoluminescence spectra study explained the rate of recombination of electron and hole pairs. The detailed magnetic study was carried out and magnetization of remanence (Mr), coercivity (Hc) & saturation (Ms) values were estimated through recording the hysteresis plots. The magnetic Mr & Ms values are noticed to be enhanced from 5.21 to 11.02 emu/g &17.37–31.37 emu/g with Ni content. Furthermore, the Cu1-xNixFe2O4 (0 ≤ x ≤ 0.5) NPs were studied by means of visible light induced RhB dye degradation and investigates major active species and a probable mechanism for degradation has been conferred. The photocatalytic activity of CuFe2O4 NPs has been improved via Ni doping. Photoluminescence spectra showed the rate of recombination of electron-hole pairs and presence of defects.

Impact of Sr2+ Dopant on Magnetic, Dielectric, and Impedance Properties of Y-Type Hexaferrite

In this paper, we investigate the magnetic, dielectric, and impedance properties of Ba2 − ySryZn2Fe12O22 (y = 0.0–1.5) hexaferrite prepared by solid-state reaction process. The magnetic hysteresis loop suggested that the prepared hexaferrite exhibits room temperature hard ferromagnetic activity. The saturation magnetization (Ms), remanence (Mr), and magneton number (nB) values are decreased with Sr2+ substitutional dopant at the Ba2+ site. On the other hand, Sr2+ doping enhances the β, Ha, and Ke values. The squareness ratio (Mr/Ms) is calculated to be 0.50, indicating the uniaxial anisotropy of BSZFO (y = 0.0–1.5) hexaferrite. Dielectric constant and dielectric loss values increased from 147 to 290 and 0.058 to 0.94, increasing Sr2+substitution from 0.0 to 1.5 at 1 MHz. This study has supported the rise in AC conductivity and decreases DC conductivity with the Sr2+ substitution.

The Evaluation of Structural, Electrical and Magnetic Properties of Samarium substituted Spinel Ferrites

The spinel ferrites have been manufacturing long time because of their variety of applications in technological and industrial field. In the following study, the samarium doped spinel ferrites were under examination. The prepared compositions were denoted as; SrSm x Fe2–x O4, x = 0, 0.025, 0.05, 0.075, 0.10. Sol–gel procedure was employed to make these samples. All the samples were investigated through the X-ray diffraction technique. The phase of prepared product was detected for the first three samples. However, the orthorhombic phase, that is, SmFeO3, was traced when samarium (Sm) composition reached 0.075 and above. The smaller width of the M–H loop confirmed the formation of soft ferrites. Saturation and remanence values were diminished with the substitution of samarium ions. But the anisotropy constant as well as coercivity values was enhanced with the samarium contents. Above mentioned features of spinel ferrites showed their possible usage in high-density recording applications.

Size-dependent magnetic hardening in CoFe2O4 nanoparticles: effects of surface spin canting

Magnetic cobalt ferrite CoFe2O4 is rich with physical phenomena, owing to its crystalline and magnetic structures. When such a ferrite is produced in a modulated nanoscale size, the increased specific surface area gives rise to even more complex behavior in its magnetism, particularly in relation to magnetic hardening. By correlating nanoparticle size (from 3.5 nm to 80 nm) with crystallite size and magnetic properties, we can observe interesting relations between particle size and magnetic coercivity. On exceeding the superparamagnetic limit of about 10 nm, room-temperature coercivity and remanence values are found to increase with increasing nanoparticle size, up to a maximum value of 4.1 kOe and 52 emu g−1, respectively, at a size of approximately 45 nm. Above this critical size, the nanoparticles are comprised of multiple crystallites, and demonstrate the existence of a cooperative phenomenon, the so-called interaction domains, which leads to a decrease in coercivity and remanence values. More interestingly, the ultrasmall-sized CoFe2O4 nanoparticles (3.5–16 nm) show an anomalous coercivity enhancement and irreversible behavior at low temperatures, as compared to the large-sized nanoparticles, which may be ascribed to enhanced effective magnetic anisotropy due to the surface spin-canting effect. Furthermore, training behavior in the exchange bias field, together with field-dependent blocking behavior, indicate that ultrasmall CoFe2O4 nanoparticles possess highly frustrated surface spins, which rearrange much more slowly than their interior spins, resulting in magnetic hardening at low temperatures.

Saccharide-capped Superparamagnetic Copper Cations-doped Magnetite Nanoparticles for Biomedical Applications: A Novel and Simple Synthesis Procedure, In-situ Surface Engineering and Characterization

Background: Recently, superparamagnetic and electromagnetic nano-materials have been extensively studied and their potential applications have also been investigated in various fields. In this regard, currently, Fe3O4 NPs are valuable candidates as diagnostic agents such as magnetic resonance imaging, enzyme immobilization, biosensing and cell labeling, and therapeutic probes, including drug delivery, bacteria detection, magnetic separation, and hyperthermia agents. Objective: In this study, electrochemical synthesis of Cu2+ cations-doped superparamagnetic magnetite nanoparticles (Cu-SMNPs) and their in situ surface coating with saccharides (i.e., glucose, sucrose and starch) are reported. The prepared glucose/Cu-SMNPs, sucrose/Cu-SMNPs and starch/Cu-SMNPs samples are characterized by structural, magnetic and morphological analyses by XRD, FT-IR, FE-SEM, EDAX and VSM. The suitability of the prepared samples for biomedical use is also proved. Methods: A simple cathodic electrochemical set-up was used to fabricate the iron oxide samples. The bath electrolyte was one litre deionized water containing 1.5g iron chloride, 3g iron nitrate, 0.5g copper chloride and 0.5g saccharide (i.e., glucose or sucrose or starch). The cathode and anode electrodes were connected to a DC power supply (PROVA 8000) as the power source. The deposition experiments were conducted at 10 mA cm-2 for 30 min. For the preparation of glucose/Cu-SMNPs, sucrose/Cu-SMNPs and starch/Cu-SMNPs samples, three electrodeposition experiments were carried out in three similar baths with only a change in the dissolved saccharide type. The prepared SMNPs samples were characterized by structural, morphological and magnetic analyses including X-ray powder diffraction (XRD, a Phillips PW-1800 diffractometer Smart Lab), field-emission scanning electron microscopy (FE-SEM, Mira 3-XMU with accelerating voltage of 100 kV), transmission electron microscopy (TEM, model Zeiss EM900 with an accelerating voltage of 80 kV), fourier transform infrared (FT-IR, a Bruker Vector 22 Fourier transformed infrared spectrometer) and vibrating sample magnetometers (VSM, model Lakeshore 7410). Results: Three types of metal-cations doped superparamagnetic magnetite nanoparticles (SMNPs), glucosegrafted Cu2+-doped MNPs (glucose/Cu-SMNPs), sucrose-grafted Cu2+-doped SMNPs (sucrose/Cu-SMNPs) and starch-grafted Cu2+-doped SMNPs (starch/Cu-SMNPs), were prepared for the first time. Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy and energy dispersive X-ray techniques proved the presence of saccharide capped layer on the surface of deposited SMNPs and also copper cations doping on their crystal structures. Superparamagnetic behaviors, including low coercivity and remanence values, were observed for all the prepared samples. Conclusion: SMNPs capped with saccharides (i.e., glucose, sucrose and starch) were successfully synthesized via one-pot simple deposition procedures. These particles showed suitable superparamagnetic properties with negligible remanence values and proper saturation magnetization, thus proving that they all have required physicochemical and magnetic characteristics for biomedical purposes.

Enhancement of sensitivity of magnetostrictive foam in low magnetic fields for sensor applications

Magnetostrictive materials are usually used in sensor technology since they are sensitive to magnetization and strain. Unfortunately, to date, only a few magnetostrictive materials are being used, as the need for a strong magnetic field (1 T) and not sensitive at a low magnetic field. Thus, in this study, a new magneto-active (MA) polyurethane foam was fabricated to obtain a strain at a low magnetic field corresponding to below 1 T. The in-situ fabrication of the MA foam was carried out with various compositions of carbonyl iron particles (CIPs), particularly at 35, 45, 55, 65 and 75 wt%. An analysis of the magnetic properties revealed that all the MA foams showed high magnetic saturation with low remanence values. Furthermore, the MA foam of 75 wt% showed the highest magnetostrictive strain of 1.66% at 0.45 T. The sensitivity of the MA foam is 0.0146%/mT with 42% of improvement. Analyses show MA foam of 75 wt% had a low density, biggest pores and long struts that might have led to high flexibility for elongation to produce a high strain percentage within the practical magnetic field range. Hence, this MA foam can be further utilized for sensor applications.

Relationship between the response of microscopic and magnetic properties with highly uniform dispersion of carbonyl iron particles in magnetorheological polyurethane foam

Magnetorheological (MR) foam, which is comprised of magnetic particles inside the matrix phase, is capable of changing its physical and rheological properties corresponding to the applied magnetic field. However, the performance of this material seems unsatisfactory due to the nonuniform distribution of magnetic particles throughout the composite area resulting in uneven magnetic properties. Since uniform magnetic properties are significant regarding MR foam, in situ fabrication using a polyvinyl chloride mould can be used to achieve the targetted improvement. MR foam was prepared with various amounts of carbonyl iron particles (CIPs), 0, 35, 45 and 55 wt%, and investigated at three different positions (top, middle and bottom parts) with a vibration sample magnetometer. The results showed that the hysteresis loop at all CIP concentrations of 35, 45 and 55 wt% exhibited superparamagnetic properties with magnetic saturation. The M s of the top, middle and bottom positions were almost the same with a small standard deviation below 2 Am2 kg–1. Moreover, it is observed that the effect of porosity results in the enhancement of the magnetic saturation and remanence values. These results reveal the promising uniform magnetic properties of MR foam, which can benefit the industry by helping produce a consistent MR foam.

Magnetic Phase Coexistence and Hard-Soft Exchange Coupling in FePt Nanocomposite Magnets.

With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe53Pt47 and Fe55Pt45, were subsequently annealed at 400 °C and 550 °C and structurally and magnetically characterized by means of X-ray diffraction, 57Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder–order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 °C, a predominant, highly ordered L10 phase is formed in both alloys, coexisting with a cubic L12 soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed. SQUID magnetometry hysteresis loops of samples annealed at 400 °C exhibit inflection points that witness the coexistence of the soft and hard magnetic phases and high values of coercivity and remanence are obtained. For the samples annealed at 500 °C, the hysteresis loops are continuous, without inflection points, witnessing complete exchange coupling of the hard and soft magnetic phases and further enhancement of the coercive field. Maximum energy products comparable with values of current permanent magnets are found for both samples for annealing temperatures as low as 500 °C. These findings demonstrate an interesting method to obtain rare earth-free permanent nanocomposite magnets with hard–soft exchange-coupled magnetic phases.

Analysis Magnetic Properties and Corrosion Resistance of Hybrid Bonded Magnet BaFe&lt;sub&gt;12&lt;/sub&gt;O&lt;sub&gt;19&lt;/sub&gt;-NdFeB

Permanent Magnets made in the form of hybrid bonded BaFe12O19 / NdFeB and with binder of Poli Vynil Alcohol (PVA) as much as 3% of the total mass in each sample. The weight ratio hybride system BaFe12O19 : NdFeB is 0 % BaFe12O19 : 100 % NdFeB ; 50% BaFe12O19 : 50 % NdFeB and 70% BaFe12O19 : 30 % NdFeB. The material preparation process was begun from mixing of raw materials using HEM for 15 minutes, then added 3% wt. of PVA. The mixed powder was formed a pellet using a hydraulic press with a force of 4 tons for 1 minute, then heated with an vacuum oven at a temperature of 110 ° C for 1 hour and the last step was magnetization using impulse magnetizer. The characterization of pellet sample was done namely measurement of bulk density, flux magnetic and hysteresis loop using VSM and then measurement of corrosion resistance of hybride bonded magnet. The characterization results show that bulk density value of sample hybride 50% BaFe12O19 – 50 % NdFeB is more larger than sample hybride 70% BaFe12O19 – 30 % NdFeB , and The highest coercivity and remanence values ​​of 3900 Oe and 2500 Gauss respectively were achieved in samples with a composition of 50% Ba-ferrite - 50% NdFeB. The hybride bonded magnet Ba-ferrite/NdFeB has more corrosion resistance than bonded magnet 100 % NdFeB.