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In this study, Mg1-xCoxFe2O4 (0max) during local magnetic hyperthermia were affected by structural alterations associated with particle size and composition. The lattice parameter, X-ray density, ionic radius, hopping length, bond length, cation-cation distance, and cation-anion distance increase with an increase in Co2+ content. Raman and FTIR spectroscopy reveal changes in cation distribution with Co2+ content and particle size. Magnetic properties measured by the physical property measurement system (PPMS) showed saturation magnetization (Ms), coercivity (Hc), remanent magnetization (Mr/Ms), and anisotropy constant (K1) of the Mg1-xCoxFe2O4 nanoparticles increase with Co2+ content and particle size. When exposed to an rf magnetic field, the nanohybrids experienced an increase in both the SLP (specific loss power) and Tmax (maximum temperature) as the particle size initially increased. However, these values reached their peak at critical particle size and subsequently decreased. This occurs since a modest increase in anisotropy, resulting from the presence of Co2+ and larger particle size, facilitates Néel and Brownian relaxation. However, for high anisotropy values and particle size, the Néel and Brownian relaxations are hindered, leading to the emergence of a critical size. The critical size increases as the Co2+ content decreases, but it decreases as the Co2+ content increases, a consequence of higher anisotropy with the increase in Co2+. Additionally, it is noteworthy that the maximum temperature (Tmax) rises as the concentration of nanohybrids grows, but the specific loss power (SLP) decreases. An increased concentration of chitosan-MCFO nanohybrids inhibits both the Néel and Brownian relaxation processes, reducing specific loss power. [ABSTRACT FROM AUTHOR]

Electro-conducting polypyrrole (PPy) coated H2N-SiO2/Ni nanocomposite particles are prepared by a three-step process. The objective is to analyze the influence of porous functional SiO2 support on the electrochemical performance of the prepared H2N-SiO2/Ni/PPy nanocomposite particles. H2N-SiO2 support is first prepared by a modified sol–gel method and then co-ordinated with Ni nanoparticles via an amine functionality. Finally, H2N-SiO2/Ni/PPy nanocomposite particles are prepared by in situ chemical oxidative polymerization of pyrrole using citric acid as a dopant. Fourier Transform IR (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed the formation of co-ordinated Ni/Ni2+ nanoparticles and a PPy layer with almost a core–shell type morphology. The mesoporous surface structure of H2N-SiO2 core-particles is confirmed from the morphological study and the specific surface area gradually decreased from 496 m2 g−1 to 59 m2 g−1 following subsequent surface modification with Ni nanoparticles and the PPy layer. The ultimate nanocomposite particles had paramagnetic properties and the magnetization value is 4.8 emu g−1. Comparative electrochemical performance between electrodes made from the respective PPy, Ni/PPy and H2N-SiO2/Ni/PPy showed the highest specific capacitance value (982.6 F g−1 from cyclic voltammetry curves) for the H2N-SiO2/Ni/PPy nanocomposite. The H2N-SiO2/Ni/PPy nanocomposite electrode is fairly stable during cycling measurement. The results indicated that the use of mesoporous functional SiO2 support remarkably improved the mechanical stability and capacitive performance of the H2N-SiO2/Ni/PPy nanocomposite electrode, suitable for application in energy storage devices. [ABSTRACT FROM AUTHOR]

We outlined cobalt ferrite (CFO) nanoparticles synthesized by chemical co-precipitation which we analyzed the structure by X-ray diffractometer (XRD) and transmission electron microscopy in the TEM and STEM mode. A STEM EDS analysis revealed elemental mapping and the stoichiometry of CoFe2O4. The particle sizes were in the range of 8–36 nm by heat treatment of the samples and coated with chitosan (CS). Mössbauer spectroscopy divulged the information that the inversion factor, d reduces with increasing particle size. The investigation of CSCFO nanoparticles on the Vero cell line appeared that the agents of different sizes were viable. Specific loss power of hyperthermia (SLP) depends strictly on the nanoparticle sizes and concentrations, which in turn govern the magnetic properties of CSCFO. We obtained the critical dimension as 18 nm, below which the heating mechanism was Néel and Brownian relaxation, and above 18 nm, the heating mechanism was hysteresis loss. The maximum temperature, Tmax, attained by the CSCFO with the concentration as low as 1 mg/ml of particle sizes 8–36 nm are 45, 52, 55, 62, and 65 °C. A quadratic variation of r2 relaxivity with the particle size, and linear variation with the magnetization indicates that the proton relaxation is consistent with the motional average regime (MAR). We inspected the CSCFO as contrast-enhancing dye for in vivo blood pool imaging demonstrated CSCFO as a good candidate for both positive and negative contrast dye. [ABSTRACT FROM AUTHOR]

Three sets of starting materials Ca(NO3)2·4H2O and (NH4)2HPO4; Ca(OH)2 and H3PO4; Ca(OH)2 and (NH4)2HPO4 were chosen for the preparation of different precursors of hydroxyapatite nanoparticles (n‐HAP) by wet chemical precipitation technique denoted by HAP‐1, HAP‐2, HAP‐3. X‐ray diffraction (XRD) studies show that n‐HAP of all three types exhibited single‐phase in the as‐prepared condition. Transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) studies of as‐prepared samples showed characteristic needle‐like particles with a width of 5 nm, which were fully crystalline exhibited by the lattice fringe in HRTEM, and single‐phase demonstrated by SAED patterns. The samples were pelletized and annealed at varying temperatures in the range of 600°C–1400°C. The results indicated that HAP‐1 and HAP‐3 samples showed phase decomposition at 1400°C to form β‐tricalcium phosphate (β‐TCP) while for HAP‐2 no such decomposition occurred up to 1400°C. Data from the Vickers hardness test revealed that the hardness value up to 2.5 GPa was attained at the sintering temperature of 1200°C for HAP‐1 and HAP‐3. The hardness values are consistently higher for HAP‐2 than HAP‐1 and HAP‐3 at all sintering temperatures and attained a value of 3 GPa at 1200°C. Thus, synthesizing n‐HAP by using H3PO4; Ca(OH)2 bestows highest Vickers hardness. [ABSTRACT FROM AUTHOR]

Frequency-dependent dielectric constant, dielectric loss, AC conductivity values and complex impedance spectra of V2O5-added Ni–Co–Zn ferrites ( Ni 0. 6 2 Co 0. 0 3 Zn 0. 3 5 Fe2 O 4 + x V2O5, where x = 0, 0.5, 1 and 1.5 wt.%) have been investigated at room temperature. The dielectric properties of the samples follow the Maxwell–Wagner polarization model. An inverse relationship was found between dielectric constant and AC electrical resistivity for all the samples. The dielectric constants decreased with the addition of V2O5, while the electrical resistivities of V2O5-added Ni–Co–Zn ferrites are found to be larger than that of pure Ni–Co–Zn ferrite. The AC conductivity was reduced with the addition of V2 O 5 to Ni–Co–Zn ferrite at lower-frequency region. However, AC conductivity shows a sharp increase at higher-frequency region, which could be attributed to the enhancement of electron hopping between the Fe 2 + and Fe 3 + ions in the ferrite matrix due to the activity of the grains. The complex impedance spectroscopy results through Cole–Cole/Nyquist plot have demonstrated a single semicircular arc. It indicates that conduction mechanism takes place predominantly through the grain/bulk property, which could be ascribed to the larger grain size of V2O5-added Ni–Co–Zn ferrites. [ABSTRACT FROM AUTHOR]

Cobalt ferrite (CoFe2O4) nanoparticles synthesized by chemical co-precipitation method were studied to see the effect of annealing temperatures on the structural parameters and magnetic properties of the sample. X-ray powder diffraction (XRD), transmission electron microscope (TEM) and SAD pattern demonstrated that single face (fcc) spinel structure of CoFe2O4 has been formed showing particles in completely crystalline state which was further confirmed by the lattice parameter and the unmixed hkl values. The particle size is in the range of about 5-10 nm depending on the annealing temperature from 200°C to 400°C. The grain growth occurred monotonically with the increase of annealing temperature. The magnetic properties demonstrated a strong dependence on particle size. The saturation magnetization Ms, remanent ratio Mr/Ms and coercivity Hc increased with the increase of particle size. The hysteresis curves for samples of different grain size showed the ferrimagnetic behavior which is completely analogous to the slow relaxation sextet peaks of Mössbauer spectroscopy. Other parameters such as chemical shift, quadruple splitting and hyperfine field and site occupancy of Fe3+ were determined by Mössbauer spectroscopy. Ferrimagnetic to superparamagnetic transition temperature known as blocking temperature TB was determined from the temperature dependent magnetization curves. With the increase of grain size, Blocking temperature also increases. Maximum entropy changes due to magnetic phase transition were also observed for mentioned annealing temperatures in the context of Magnetocaloric effect. [ABSTRACT FROM AUTHOR]

A detailed study of magnetic softness has been performed on FINEMENT type of ribbons by investigating the BH loop with maximum applied field of 960 A/m. The ribbon with the composition of Fe74Cu0.8Nb2.7Si15.5B7 was synthesized by rapid solidification technique and the compositions volume fraction was controlled by changing the annealing condition. Detail phase analysis was performed through X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Vibrating sample magnetometer (VSM) and Mössbauer spectroscopy in order to correlate the ultrasoft magnetic properties with the volume fraction of amorphous and α-Fe(Si) soft nano composites. Bright (BF) and dark field (DF) image with selective area diffraction (SAD) patterns by the transmission electron microscopy (TEM) of the sample annealed for the optimized annealed condition at 853 K for 3 min reveals nanocrystals with an average size between 10-15 nm possessing the bcc structure which matches with the grain size revealed by the X-ray diffraction. Kinetics of crystallization of α-Fe(Si) phases has been determined by DSC curves. Extremely small coercivity of 30.9 A/m and core loss of 2.5 W/Kg for the sample annealed at 853 K for 3 min was found. Similar values for other crystalline conditions were determined by using BH loop tracer with a maximum applied field of around 960 A/m. Mössbauer spectroscopy was used to determine chemical shift, hyperfine field distribution (HFD), and peak width of different phases. The volume fractions of the relative amount of amorphous and crystalline phases are also determined by Mössbauer spectroscopy. High saturation magnetization along with ultrasoft magnetic properties exhibits very high potentials technological applications. [ABSTRACT FROM AUTHOR]