Considerable Saturation Magnetization Research Articles

Coexistence of high magnetic and dielectric properties in Ni-Zr co-doped barium hexaferrites

Increased demands for multifunction, integration and miniaturization of electronic devices lead to the investigation of M-type hexaferrite with more abundant properties. In this paper, Ni-Zr co-doped barium ferrite (BaFe 12–2 x Ni x Zr x O 19 , 0 ≤ x ≤ 1 with step of 0.2) with concurrent of considerable saturation magnetization and dielectric properties are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM) and LCR meter. Results reveal that pure M-type hexaferrite phase are obtained with expanded cell parameters by increasing Ni-Zr substitution content. The microstructure shows that Ni-Zr doping has small influence on the average grain size. Magnetic measurements indicate that a maximum saturation magnetization is obtained at x = 0.2 with considerable value of 71.5 emu/g. While the permittivity is substantially enhanced by Ni-Zr co-doping for barium hexaferrite with values reach up to ~10 3 at 100 kHz and dielectric tangent loss about 0.2. These results imply that Ni-Zr doped barium hexaferrites may have potential application in multifunctional and miniaturized electronic devices. • Considerable saturation magnetization with values of 50-71.5 emu/g are obtained for Ni-Zr co-doped BaFe 12 O 19 . • Enhanced dielectric constant up to 10 3 at high frequency with low dielectric tangent loss about 0.2 is obtained. • The mechanism for the influence of Ni-Zr doping on the magnetic and dielectric behaviors of BaFe 12 O 19 have been analyzed.

One-pot solvothermal synthesis of magnetically separable rGO/MnFe2O4 hybrids as efficient photocatalysts for degradation of MB under visible light

Efficient and easily separable photocatalysts with visible light response are of great importance for the degradation of organic pollutants in wastewater treatment. In this work, magnetically separable reduced graphene oxide (rGO) supported MnFe2O4 hybrids were prepared using graphene oxide and metal ions (Fe3+ and Mn2+) as starting materials via a one-pot solvothermal synthesis method. The hybrids were characterized by X-ray powder diffraction, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, Fourier Transform Infrared Spectroscopy, Ultraviolet–visible spectroscopy, and vibrating sample magnetometer. The influence of the rGO content on the morphology and catalytic performance was investigated. It was shown that monodispersed MnFe2O4 microspheres with uniform size were successfully embedded in the rGO nanosheets. The photocatalytic activity has been evaluated by photocatalytic degradation of methylene blue under visible light irradiation. Among the hybrids with various rGO contents, the hybrid (10% rGO/MnFe2O4) prepared with 10 wt% GO showed the best performance with reaction rate of 0.01443 min−1, around 6 times higher than that of MnFe2O4 (0.00248 min−1), demonstrating the important role of rGO for the photocatalytic activity. Benefiting from their considerable saturation magnetization, lower remanence and coercivity, the hybrids can be easily separated and recycled from the solution by an external magnet. This research would provide a strategy for designing efficient and magnetically recycled photocatalysts for wastewater decontamination under visible light.

Structure and magnetic analyses of hexaferrite Sr1−xLaxFe22+Fe163+O27 prepared via the solid-state reaction

W-type ferrite Sr1−xLaxFe22+Fe163+O27 (x = 0.00, 0.05, 0.08, 0.10, 0.13 and 0.15) powders and magnets were prepared via the solid-state reaction in nitrogen. Phase components of the powder samples were examined by X-ray diffraction (XRD). XRD results demonstrated the appearance of pure phase hexagonal crystal structure and calculate the lattice constants c and a, c/a ratio, cell volume (Vcell), X-ray density (dX-ray) and crystallite size (D) parameters according to XRD data. Scanning electron microscopy (SEM) was used to observe the morphology of the magnets. SEM analyses revealed the hexagonal morphology of the ferrites. The magnetic characteristics of magnetic powders were measured by a vibrating sample magnetometer (VSM), and the magnetic characteristics of magnets were also measured by a permanent magnetic measuring equipment. The results indicate that, the synthesized samples with a low coercive force value and a considerable saturation magnetization are best able to make optical read-out of the magnetic storage information in erasable video and audio discs.

Structure, magnetic and cytotoxic behaviour of solvothermally grown Fe3O4@Au core-shell nanoparticles

Magnetic nanoparticles (MNPs) have demonstrated their potential in a wide variety of biomedical applications including in tumour hyperthermia. However, highly reactive nature and aggregation affinity of these nanostructures are the principal limitations for such applications. To overcome these limitations, those MNPs should be covered with an inert shell in order to protect the magnetic core against chemical alterations. Considering the noble, chemically inert nature of gold, which also has good biocompatibility, we fabricated chemically stable gold-coated Fe3O4 (Fe3O4@Au) nanoparticles of 20–50 nm size range with considerable saturation magnetization, though a simple one-pot solvothermal method. The morphology, elemental distribution and the structure of the core-shell nanoparticles were characterized using aberration-corrected (Cs) Scanning transmission electron microscopy (STEM), and compared with their simulated images. Cytotoxicity assay in MDCK cell line was performed to evaluate the biocompatibility of the nanoparticles. The results showed higher cell viability for the Fe3O4@Au nanoparticles, suggesting their good biocompatibility and potentials for biomedical applications.

The synthesis of Cu/Fe/Fe3O4 catalyst through the aqueous solution ball milling method assisted by high-frequency electromagnetic field

In this paper, nano-magnetic Cu/Fe/Fe3O4 catalyst was prepared by a new aqueous solution ball milling method assisted by high-frequency electromagnetic field at room temperature. The products were characterized by means of X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), selected area electron diffraction (SAED), and vibrating sample magnetometer (VSM). Microwave induced catalytic degradation of methylene blue (MB) was carried out in the presence of Cu/Fe/Fe3O4. The concentration of methylene blue was determined by UV–Vis spectrophotometry. The solid catalyst showed high catalytic activity of degrade MB and considerable saturation magnetization, lower remanence and coercivity. It indicate that the catalyst can be effectively separated for reuse by simply applying an external magnetic field and it can greatly promote their potential industrial application to eliminate organic pollutants from waste-water. Finally, we found that it is the non-thermal effect of microwave that activated the catalytic activity of Cu/Fe/Fe3O4 to degrade MB.

Controlling the size and magnetic properties of nano CoFe2O4 by microwave assisted co-precipitation method

In this report, cobalt ferrite nanoparticles synthesized using microwave assisted co-precipitation method was reported. Efforts have been made to control the particles size, distribution, morphology and magnetic properties of cobalt ferrite nanoparticles by varying the concentration of NaOH solution and microwave irradiation time. It was observed that the rate of nucleation and crystal growth was influenced by the tuning parameters. In that way, the average crystallite size of single phase cobalt ferrite nanoparticles was controlled within 9–11 and 10–12 nm with an increase of base concentration and microwave irradiation time, respectively. A narrow size distribution of nearly spherical nanoparticles was achieved through the present procedure. A soft ferromagnetism at room temperature with the considerable saturation magnetization of 58.4 emu g−1 and coercivity of 262.7 Oe was obtained for the cobalt ferrites synthesized with 2.25 M of NaOH solution for 3 and 7 min of microwave irradiation time, respectively. The cobalt ferrite nanoparticles synthesized with a shorter reaction time of 3–7 min was found to be advantageous over other methods that involved conventional heating procedures and longer reaction time to achieve the better magnetic properties for the technological applications.

Influence of sputtering power on structural and magnetic properties of as-deposited, annealed and ERTA Co2FeSi films: A comparative study

We report the effect of sputtering power (200 W - 350 W) on the structural, topographical and magnetic properties of Co2FeSi (CFS) films deposited at ambient temperatures as compared to the films which were either annealed at 300 °C or were subjected to Electron beam Rapid Thermal Annealed (ERTA) treatment. The structural and morphological analyses reveal changes in their crystalline phases and particle sizes. All the as-deposited and annealed CFS films showed A2 phase crystal structure. Whereas the CFS film sputtered at 350 W followed by ERTA displayed the fully ordered L21 structure. The particles are spherical in shape and their sizes increased gradually with increase in the sputtering power of the as-deposited and annealed CFS films. However, ERTA CFS films had spherical as well as columnar (elongated) shaped grains and their grain sizes increased nonlinearly with sputtering power. M-H studies on as-deposited, annealed and ERTA CFS films show ferromagnetic responses. The comparatively stronger ferromagnetic response was observed for the ERTA samples with low saturation field which depends on the enrichment of fine crystallites in these films. This indicates that, apart from higher sputtering powers used for deposition of CFS films, ERTA process plays a significant role in the enhancement of their magnetic responses. 350 W ERTA film has the considerable saturation magnetization (∼816 emu/cc), coercivity (∼527 Oe) and a good squareness values at 100 K than at 300 K, which could originate from the spin wave excitation effect. Further, the optimized parameters to achieve a CFS film with good structural and magnetic properties are discussed from the perspective of spintronics.

Highest coercivity and considerable saturation magnetization of CoFe2O4 nanoparticles with tunable band gap prepared by thermal decomposition approach

The report states that well-dispersed CoFe2O4 nanoparticles (NPs) with controllable morphology were prepared using an economical and facile one-pot thermal decomposition approach. Cobalt (II) acetylacetonate and Iron (III) acetylacetonate were employed as precursors instead of expensive and toxic pentacarbonyl. The transmission electron microscopy and powder X-ray diffraction investigation show that CoFe2O4 NPs possess cubic morphology, homogeneous size distribution and pure phase structure. Optical band gap was tuned from 1.147 to 0.92 eV and saturation magnetization (M s) increased from 53.91 to 84.01 emu/g for the as-prepared and annealed (700 °C) NPs. The coercivity (H c) enhanced from 1137 to 2109 Oe at room temperature, which is the highest value reported to date for CoFe2O4 NPs synthesized by thermal decomposition. All CoFe2O4 (as-prepared and annealed) NPs showed excellent ferromagnetism behaviour at room temperature. Raman studies of CoFe2O4 NPs confirm the redistribution of Co2+ from octahedral to tetrahedral site. The work demonstrates the great potential of CoFe2O4 NPs as a promising alternative for data storage device applications as well as for opto-magnetic devices.

Synthesis, microstructure and magnetic performance of FeCo alloy nanoribbons

In this letter, we reported a novel FeCo alloy nanoribbon successfully synthesized via an electrospinning route followed by air-annealing at first and then deoxidizing in a mixture of H2 and Ar. The results not only revealed that the as-deoxidized FeCo alloy nanoribbons were self-assembled by abundant well-crystallized FeCo alloy nanoparticles and exhibited the excellent soft magnetic performance with considerable saturation magnetization, but also claimed that the deoxidization temperature had a significant influence on the ribbon-structures and magnetic properties. We expected that this work could open a new insights into the architectural design of magnetic alloy materials.

Improved coercivity and considerable saturation magnetization of cobalt ferrite (CoFe2O4) nanoribbons synthesized by electrospinning

Cobalt ferrite (CoFe2O4) nanoribbons with high crystallinity and purity were synthesized by annealing the as-spun PVP/[Co(NO3)2+Fe(NO3)3] precursor nanoribbons at temperatures from 450 to 750 °C in air, and they were certified to have an improved coercivity (Hc) and considerable saturation magnetization (Ms). Although all the prepared CoFe2O4 nanoribbons presented an excellent ferromagnetism behavior at room temperature, their Ms progressively increased with increasing annealing temperature but Hc followed an opposite variation tendency. The maximum Ms of about 80.3 emu g−1 of the nanoribbons annealed at 750 °C was basically equal to the bulk value, and the maximum Hc of about 1802 Oe of the nanoribbons annealed at 450 °C, is larger than most of reported Hc values of other one-dimensional CoFe2O4 nanostructures by far. It suggested that the magnetization reverse processes of the CoFe2O4 nanoribbons annealed at 450 and 550 °C were dominated by the coherent rotation model, while that of the CoFe2O4 nanoribbons annealed at 650 and 750 °C were dominated by the growth of a reverse magnetic domain.

In situ growth of hollow CuNi alloy nanoparticles on reduced graphene oxide nanosheets and their magnetic and catalytic properties

Hollow CuNi nanocrystals supported on reduced graphene oxide (RGO–CuNi) are synthesized by in situ co-reduction of Cu2+, Ni2+ and graphene oxide (GO) in a one-pot reaction. The as-synthesized RGO–CuNi nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry, inductively coupled plasma optical emission spectrometry, Raman spectroscopy, and magnetic measurement. It is revealed that hollow CuNi nanocrystals with an average size of about 35.1nm are uniformly deposited on the surface of RGO nanosheets. The formation mechanism of the hollow CuNi nanostructures is also proposed based on the galvanic displacement reaction. The as-synthesized RGO–CuNi nanocomposite exhibits excellent electrocatalytic performance toward the oxidation of glucose in alkaline media, and also shows superior catalytic activity and recycling stability toward the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Moreover, the RGO–CuNi catalysts can be easily recollected from the reaction system by an external magnetic field due to their considerable saturation magnetization. It is anticipated that loading hollow nanostructures on RGO sheets would open up a new avenue for developing multifunctional catalysts with low cost and high catalytic performance.

One-pot solvothermal preparation of magnetic reduced graphene oxide-ferrite hybrids for organic dye removal

A one-pot solvothermal synthesis method was developed to prepare reduced graphene oxide (RGO) supported ferrite (MFe2O4, M=Mn, Zn, Co and Ni) hybrids using graphite oxide and metal ions (Fe3+ and M2+) as starting materials. The hybrids were characterized by X-ray powder diffraction, Raman spectra, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and vibrating sample magnetometer. It was shown that monodispersed MFe2O4 microspheres with uniform size were homogeneously deposited on RGO nanosheets. The influence of the metal ion concentration on the morphology of the hybrids was investigated. The hybrids possess considerable saturation magnetization, lower remanence and coercivity. Importantly, the obtained hybrids are effective adsorbents for removal of dye pollutants. It was found that over 92% rhodamine B (RhB) and 100% methylene blue (MB) with a concentration of 5mg/L can be removed by the hybrids within 2min when the concentration of the hybrids is 0.6g/L. In addition, the hybrids also show enhanced photocatalytic activity in the degradation of RhB and MB. Benefiting from their bigger saturation magnetization, the hybrids can be easily separated from the solution by a magnet. This research would provide a new easy separating platform for wastewater decontamination.

One-step preparation of hierarchical superparamagnetic iron oxide/graphene composites via hydrothermal method

In this paper, graphene/magnetite composites with hierarchical Fe3O4 structures were synthesized via a one-step hydrothermal method. The size of Fe3O4 nanocrystals and nanocrystal clusters can easily be controlled by altering reaction time and the starting mixed solvent ratio, respectively. Raman measurements evidenced that graphene oxide was simultaneously reduced to graphene during the deposition of magnetite particles. The deposition of Fe3O4 nanocrystals and nanocrystal clusters impedes graphene to restore the graphite structure. The composites showed a high crystallinity of magnetite and a considerable saturation magnetization. Furthermore, the acrylate modified Fe3O4 makes the composites water-dispersible and can effectively load polyfluorene polyelectrolyte via electrostatic force. The high magnetism, excellent water dispersibility and strong photoluminescence make these composites ideal candidates for various important applications such as magnetic resonance imaging, bioseparation, bioimaging, and optical devices fabrication.

One-pot preparation of graphene/Fe3O4 composites by a solvothermal reaction

A one-pot solvothermal reaction was used to prepare graphene/Fe3O4 composites using graphite oxide and FeCl3·6H2O as starting materials. Graphene oxide was reduced to graphene and the Fe3O4 microspheres were simultaneously grown on the carbon basal planes under the conditions generated in the solvothermal system. The product showed a high crystallinity of magnetite and a considerable saturation magnetization. The size and density of the Fe3O4 microspheres distributed on the graphene can be easily controlled by altering the starting Fe3+ concentration. Doxorubicin hydrochloride was loaded on to the graphene/Fe3O4 composites by simple mixing, and a saturation loading capacity as high as 65% could be achieved.

A Structural and Magnetic Study of the Series of Double Perovskites Ca2Fe1+xW1–xO6

AbstractThe synthesis of the Ca2Fe1+xW1–xO6 perovskite solid solution in the range x = 0.13–0.33 by a soft‐chemistry procedure followed by annealing at different temperatures under different reducing atmospheres, and its characterization by X‐ray and neutron diffraction together with magnetic measurements, is reported. The average Fe oxidation state in this series varies smoothly from Fe2.46+ in Ca2Fe1.13W0.87O6 to Fe3+ in Ca2Fe1.33W0.67O6. A detailed description of the crystal structure of four selected members of this series (x = 0.2, 0.23, 0.30, 0.33) is provided. All these compounds crystallize in the space group P21/n, with a ≈ b ≈ √2a0 and c ≈ 2a0, although they show different levels of long‐range ordering between the two different cations placed at the B positions of the A2B′B″O6 perovskite structure. The driving force for this B′/B″ ordering is the charge difference between both kinds of cations, whereby the earlier members of the series, which contain a large proportion of Fe2+, are fully ordered whereas a strong antisite disorder effect is observed for the later members. The evolution of this antisite disordering has a dramatic influence on the magnetic properties across the series. Thus, for x = 0.20, the ferrimagnetic Curie temperature is above 400 K, although the saturation magnetization is very low, since there is a poor coherence between the antiferromagnetic patches formed by Fe–O–Fe interactions between the B′ and B″ positions of the perovskite, whereas the x = 0.33 compound, which has a lower TC of 310 K, shows a considerable saturation magnetization and a surprisingly strong magnetic neutron scattering for such a structurally disordered sample. The observed scattering can be ascribed to the good coherence obtained via Fe–O–Fe superexchange interactions among the Fe‐rich, antiferromagnetically ordered patches that occur naturally thorughout the crystal. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Microstructural, thermal and magnetic properties of amorphous/nanocrystalline FeCrMnN alloys prepared by mechanical alloying and subsequent heat treatment

Amorphous FeCrMnN alloys were synthesized by mechanical alloying (MA) of the elemental powder mixtures under a nitrogen gas atmosphere. The phase identification and structural properties, morphological evolution, thermal behavior and magnetic properties of the mechanically alloyed powders were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively. According to the results, at the low milling times the structure consists of the nanocrystalline ferrite and austenite phases. By progression of the MA process, the quantity and homogeneity of the amorphous phase increase. At sufficiently high milling times (>120 h), the XRD pattern becomes halo, indicating complete amorphization. The results also show that the amorphous powders exhibit a wide supercooled liquid region. The crystallization of the amorphous phase occurs during the heating cycle in the DSC equipment and the amorphous phase is transformed into the crystalline compounds containing ferrite, CrN and Cr 2N. The magnetic studies reveal that the magnetic coercivity increases and then decreases. Also, the saturation magnetization decreases with the milling time and after the completion of the amorphization process (>120 h), the material shows a paramagnetic behavior. Although the magnetic behavior does not considerably change by heating the amorphous powders up to the crystallization temperature via DSC equipment, the material depicts a considerable saturation magnetization after the transformation of the amorphous phase to the nanocrystalline compounds.