Ferrite Nanostructures Consolidated by Spark Plasma Sintering (SPS)

Ferrites are a well-known class of ferrimagnetic materials. In the form of nanoparticles (NPs), they exhibit novel and fascinating properties, leading to an extremely wide variety of applications in electronics, biomedical and environmental fields. These applications result from nanoscale effects on physical properties, particularly magnetic properties. For applications in electronic devices, however, a high-density, consolidated body, with very fine grains is needed, in order to retain the nanoscale properties. To our knowledge, spark plasma sintering (SPS) is the only method permitting a full densification with final grain size in the nanometer range. In this review, we examine the SPS method as applied to ferrites and, in particular, the effects of SPS parameters on the final nanostructures obtained. Due to their technological impact, we also discuss the SPS fabrication of hybrid multiferroic nanostructures composed of a ferrite and a ferroelectric phase

Giant Barkhausen jumps in exchange biased bulk nanocomposites sinterd fom core-shell Fe3O4-CoO nanoparticles

International audienceThe magnetic behavior of spark plasma sintered Fe3O4-CoO nanoparticles is studied. The samples sintered at 500°C exhibit density over 90% and average magnetite grain size about 100 nm. When the nanocomposite is field cooled below the Néel temperature (TN=291 K for CoO), hysteresis loops shows the expected shift with an exchange field of 80 mT at 100 K that drops down to zero approaching TN. The coercivity at 100 K reaches 0.4 T, ten times larger than nanostructured magnetite prepared in the same conditions. When the sample is zero field cooled down to 90 K, the hysteresis loops exhibits giant Barkhausen jumps, an anomalous feature never observed before to our knowledge. The density of jumps gradually decrease on heating and disappear between 150 and 170 K. The stochastic character of the jumps is visible in the plot of the differential permeability. This new phenomenon is thought that it could be related to self-field cooling

Sintering and Reactive Sintering by Spark Plasma Sintering (SPS)

A wide variety of technological applications, especially in electronics, requires high‐density nanostructured solids, consolidated by sintering from nanoparticles. A new sintering technique known as spark plasma sintering (SPS) appears as the only method to reach high densities while preserving the final grain size within the nanometric range, with the added advantage of carrying out the process at significantly lower temperatures and shorter times as compared with the classical processes. Recent studies have revealed that in many cases, SPS can also accomplish the solid‐state reaction to achieve the desired compound, leading to reactive SPS (RSPS). In this chapter, a review of RSPS is presented, focusing particularly on magnetic oxide materials as functional solids

Humidity and Temperature Sensing of Mixed Nickel–Magnesium Spinel Ferrites

Temperature- and humidity-sensing properties were evaluated of NixMg1-x spinel ferrites (0 ≤ x ≤ 1) synthesized by a sol-gel combustion method using citric acid as fuel and nitrate ions as oxidizing agents. After the exothermic reaction, amorphous powders were calcined at 700 °C followed by characterization with XRD, FTIR, XPS, EDS and Raman spectroscopy and FESEM microscopy. Synthesized powders were tested as humidity- and temperature-sensing materials in the form of thick films on interdigitated electrodes on alumina substrate in a climatic chamber. The physicochemical investigation of synthesized materials revealed a cubic spinel Fd3¯m phase, nanosized but agglomerated particles with a partially to completely inverse spinel structure with increasing Ni content. Ni0.1Mg0.9Fe2O4 showed the highest material constant (B30,90) value of 3747 K and temperature sensitivity (α) of −4.08%/K compared to pure magnesium ferrite (B30,90 value of 3426 K and α of −3.73%/K) and the highest average sensitivity towards humidity of 922 kΩ/%RH in the relative humidity (RH) range of 40–90% at the working temperature of 25 °C

Ferroelectric, Magnetic and Dielectric Properties of SrCo0.2Zn0.2Fe11.6O18.8 Hexaferrite Obtained by “One-Pot” Green Sol-Gel Synthesis Utilizing Citrus reticulata Peel Extract

SrCo0.2Zn0.2Fe11.6O18.8 hexaferrite was obtained by a “one-pot” green sol-gel synthesismethod utilizing aqueous mandarin orange (Citrus reticulata) peel extract as an eco-friendly reactant.The research objective was to analyze the influence of cobalt and zinc co-doping and the synthesisprocess on the structure, morphology, magnetic, dielectric and ferroelectric properties of strontiumhexaferrite in view of future applications. Structural and morphological characterization usingX-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electronmicroscopy coupled to energy dispersive X-ray spectrometry (SEM-EDX) confirmed the formationof a Co and Zn ion incorporated M-type magnetoplumbite with c/a lattice parameter ratio of 3.919as crystallite nanoplatelets of 32 and 53 nm in thickness and width, respectively. The magnetichysteresis loop of the synthesized powder recorded by a vibrating sample magnetometer (VSM) atroom temperature confirmed its ferromagnetic nature with a coercive field (Hc) of 2539 Oe and asaturation magnetization (Ms) and remanent magnetization (Mr) of 44.6 emu/g and 21.4 emu/g,respectively. Room temperature ferroelectric loops measured at 100 Hz showed a maximal (Pmax)and a remanent (Pr) polarization of 195.4 and 31.0 nC/cm2, respectively. Both increased when themagnitude of the applied electrical field increased in the 1–24 kV/cm range. The dielectric constantdecreased with the frequency increase, in accordance with the Maxwell–Wagner model, while theconductivity changed according to the Jonscher power law. The complex impedance was modeledwith an equivalent circuit, enabling identification of the dominant contribution of grain boundaryresistance (272.3 MW) and capacitance (7.16 pF)

Lamellar nickel hydroxy-halides: anionic exchange synthesis, structural characterization and magnetic behavior:

Nickel-layered hydroxy-halides LHS-Ni-X (X = Cl, Br, and I) have been prepared by exchange reactions conducted in an aqueous medium under an inert atmosphere starting from the parent nickel-layered hydroxyacetate. The latter was prepared by a hydrolysis reaction conducted in a polyol medium. IR and X-ray diffraction (XRD) studies show total exchange. These compounds exhibit a brucite-like structure with a turbostratic nature. Their interlamellar distance varies linearly with the radius of the halide anion in the range 7.9-8.7 angstrom while the hydroxyacetate interlamellar distance is 10.53 angstrom. In comparison with the acetate ion which replaces hydroxyl groups in the brucite-like layer, EXAFS and XRD investigations show that halide ions are intercalated into the interlayer space along with water molecules without any covalent bonding to the nickel ion. All compounds have similar structural features and can be considered as alpha-type nickel hydroxides, alpha-Ni(OH)(2). These compounds exhibit a ferromagnetic character. The latter is discussed on the basis of the Drillon-Panissod model of ferromagnetic layers interacting via dipole interactions and taking into account the structural features established by XANES and XRD studies along with the intrinsic properties of the halide anions

Magnesium substitution with nickel and its influence on the sensing properties of MgFe2O4

Mixed spinel ferrites MgxNi1-xFe2O4 were synthesized via sol-gel combustion synthesis with citric acid as fuel, followed by calcination at 700 °C for 3 hours. Obtained powders were characterized via X-ray diffraction analysis (XRD), X-ray photoelectron (XPS), FTIR and Raman spectroscopy and FESEM microscopy. Elemental composition was examined via energy dispersive spectroscopy (EDS). Humidity sensing properties were tested by measuring AC impedance in a climactic chamber at 25 °C and in the relative humidity range of 40–90%. Temperature sensing properties were tested by measuring DC resistance at 40% RH in the temperature range 40–90 °C. Synthesized powders were proven to be pure spinel Fd 3m phase with spherical, slightly agglomerated particles. Substitution of Mg with Ni results in structural changes such as a change in inversion parameter and particle agglomeration, which influences sensing properties of the material. Results show that the sensing properties of magnesium ferrite, which is already a well-established NTC sensor, can be improved by incorporating 10% of nickel in the spinel lattice structure. Mg0.9Ni0.1Fe2O4 exhibited higher temperature sensitivity and higher sensitivity towards humidity compared to MgFe2O4, while further substitution of Mg with Ni resulted in the decline of sensing properties, increase in particle size and agglomeration degree

Humidity and Temperature Sensing of Mixed Nickel–Magnesium Spinel Ferrites

Temperature- and humidity-sensing properties were evaluated of NixMg1-x spinel ferrites (0 ≤ x ≤ 1) synthesized by a sol-gel combustion method using citric acid as fuel and nitrate ions as oxidizing agents. After the exothermic reaction, amorphous powders were calcined at 700 °C ollowed by characterization with XRD, FTIR, XPS, EDS and Raman spectroscopy and FESEM icroscopy. Synthesized powders were tested as humidity- and temperature-sensing materials in the form of thick films on interdigitated electrodes on alumina substrate in a climatic chamber. The physicochemical investigation of synthesized materials revealed a cubic spinel Fd3m phase, nanosized but agglomerated particles with a partially to completely inverse spinel structure with increasing Ni content. Ni0.1Mg0.9Fe2O4 showed the highest material constant (B30,90) value of 3747 K and temperature sensitivity (α) of −4.08%/K compared to pure magnesium ferrite (B30,90 value of 3426 K and α of −3.73%/K) and the highest average sensitivity towards humidity of 922 kΩ/%RH in the relative humidity (RH) range of 40–90% at the working temperature of 25 °C

Magnesium substitution with nickel and its influence on the sensing properties of MgFe2O4

Mixed spinel ferrites MgxNi1-xFe2O4 were synthesized via sol-gel combustion synthesis with citric acid as fuel, followed by calcination at 700 °C for 3 hours. Obtained powders were characterized via X-ray diffraction analysis (XRD), X-ray photoelectron (XPS), FTIR and Raman spectroscopy and FESEM microscopy. Elemental composition was examined via energy dispersive spectroscopy (EDS). Humidity sensing properties were tested by measuring AC impedance in a climactic chamber at 25 °C and in the relative humidity range of 40–90%. Temperature sensing properties were tested by measuring DC resistance at 40% RH in the temperature range 40–90 °C. Synthesized powders were proven to be pure spinel Fd 3m phase with spherical, slightly agglomerated particles. Substitution of Mg with Ni results in structural changes such as a change in inversion parameter and particle agglomeration, which influences sensing properties of the material. Results show that the sensing properties of magnesium ferrite can be improved by incorporating 10% of nickel in the spinel lattice structure. Mg0.9Ni0.1Fe2O4 exhibited higher temperature sensitivity and higher sensitivity towards humidity compared to MgFe2O4, while further substitution of Mg with Ni resulted in the decline of sensing properties, increase in particle size and agglomeration degree

Magnesium substitution with nickel and its influence on the sensing properties of MgFe2O4

Mixed spinel ferrites MgxNi1-xFe2O4 were synthesized via sol-gel combustion synthesis with citric acid as fuel, followed by calcination at 700 °C for 3 hours. Obtained powders were characterized via X-ray diffraction analysis (XRD), X-ray photoelectron (XPS), FTIR and Raman spectroscopy and FESEM microscopy. Elemental composition was examined via energy dispersive spectroscopy (EDS). Humidity sensing properties were tested by measuring AC impedance in a climactic chamber at 25 °C and in the relative humidity range of 40–90%. Temperature sensing properties were tested by measuring DC resistance at 40% RH in the temperature range 40–90 °C. Synthesized powders were proven to be pure spinel Fd 3m phase with spherical, slightly agglomerated particles. Substitution of Mg with Ni results in structural changes such as a change in inversion parameter and particle agglomeration, which influences sensing properties of the material. Results show that the sensing properties of magnesium ferrite, which is already a well-established NTC sensor, can be improved by incorporating 10% of nickel in the spinel lattice structure. Mg0.9Ni0.1Fe2O4 exhibited higher temperature sensitivity and higher sensitivity towards humidity compared to MgFe2O4, while further substitution of Mg with Ni resulted in the decline of sensing properties, increase in particle size and agglomeration degree