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In this report, a detailed investigation of magnetocaloric properties of Ce 3 + -doped zinc–cobalt spinel ferrite nanoparticles with the generic formula Zn 0.6 Co 0.4 Ce x Fe 2 - x O 4 (x = 0.02 , 0.04 , 0.06) synthesized via chemical coprecipitation method had been carried out. Rietveld analysis of the X-ray diffraction (XRD) patterns confirmed the phase purity of the nanoparticles and the corresponding space group was found to be Fd 3 ¯ m for the series. The shift of microstrain inside the crystal from compressive to tensile regime with doping of Ce confirms the expansion of unit cell in the whole series. Raman spectroscopy also confirmed the spinel structure of the samples. Coexistence of magnetic phases below room temperature is observed from the magnetization measurements with temperature under 500 Oe applied field. A decrease in T C as well as T B was observed with increase in x due to weakening of exchange interaction. The transition temperature of Ce-04 nanoparticles is quite close to room temperature which may be beneficial for room temperature magnetic refrigeration. Though the Ce 3 + doping in the series did not favour enhancement of magnetic entropy change, it enhanced the RCP which could be beneficial for room temperature or below room temperature magnetic refrigeration. A good correlation was established between magnetocaloric properties and critical behaviour of Ce 3 + -doped zinc–cobalt spinel ferrite nanoparticles. [ABSTRACT FROM AUTHOR]

This paper reports the effects of rare-earth Sm3+ ion substitution on structural, optical, electronic, and magnetic responses of maghemite nanoparticles. Four samples of varying Sm ion percentage (γ-Fe2-xSmxO3: x = 0.00, 0.02, 0.04, and 0.06) were prepared using chemical co-precipitation route. Generation of cubic spinel structure of synthesized nanoparticles was confirmed by analyzing the X-ray diffraction patterns. Average sizes of synthesized nanocrystals were calculated in between 11 and 18 nm together with the presence of compressive-type microstrain inside the tiny crystals was noticed. All the samples exhibited excellent absorption around red and infrared band of EM spectra at 300 K. Room temperature M-H response revealed a gradual reduction in several magnetic parameters like coercivity, magnetic moment, effective anisotropy constant, and saturation magnetization for higher Sm ion content samples. AC conductivity studies at room temperature suggested that the hopping of electrons in between the cationic sites was the primary charge transfer process for all the samples. [ABSTRACT FROM AUTHOR]

Proper correlation among the microstructural, optical and magnetic responses of Fe-doped ZnO nanoparticles has been established in this work. All the Fe-doped ZnO nanoparticles (Zn1−xFexO: x = 0.00, 0.05, 0.10 and 0.15) were prepared using chemical co-precipitation route. Average crystallites size of 18 nm to 28 nm was estimated using Scherrer's formula. Compressive microstrain was detected in pristine ZnO samples, which moved toward tensile regime upon introducing Fe ions of different weight percentages. Mean crystallites size obtained from Scherrer's formula was found in almost exact match with the particle size estimated from HRTEM images. Nearly spherical ZnO nanoparticles were seen in HRTEM images and negligible agglomeration among particles was also observed. Direct optical band gaps were found in the range of 2.89–3.24 eV as estimated from Tauc plots. A decent ferromagnetic signature in non-magnetic ZnO nanoparticles was also introduced at room temperature with the doping of Fe ions. [ABSTRACT FROM AUTHOR]

This paper describes the composition-dependent microstructural, magnetic and dielectric properties of vanadium ions doped nickel ferrite nanoparticles. All the nanoferrite samples (NiVxFe2-xO4: x = 0.00, 0.05, 0.10 and 0.15) were prepared using conventional co-precipitation method. X-ray diffraction patterns verified the single cubic spinel phase formation and achievement of nanosized ferrite particles with a homogeneous distribution, which was also supported by HRTEM micrographs. Mean crystallite diameter was seen in the range of 05 nm to 12 nm as evaluated from Williamson-Hall (W-H) curves for the different doped samples. A compressive nature microstrain was noticed in all the samples and was also seen to reduce with the enhancement of vanadium ions content. A blue shift was detected in the indirect band gap for higher vanadium doped samples. Magnetization at the saturation point as well as coercive field both were observed to reduce at room temperature with increasing vanadium concentration in nanosized nickel ferrites. Room temperature dielectric characteristics of all the synthesized samples ensured that the elementary charge conduction process was governed by the hopping of electrons. Cole-Cole plots also showed that the grain boundaries play an important task in deciding the dielectric responses. [ABSTRACT FROM AUTHOR]

In this article, indium ion-doped mixed nickel–cobalt ferrite nanoparticles with chemical composition Ni0.7Co0.3InxFe2−xO4 (x = 0.00, 0.05, 0.10, 0.15 and 0.30) were synthesized using soft co-precipitation method. All prepared nanoferrites showed pure cubic spinel structure without containing any impurity phases as ensured by X-ray diffraction profiles. Mean diameters of nanocrystals were found within the range of 5 nm to 13 nm as estimated from Williamson–Hall (W–H) plots. Due to large size of In3+ ions, the compressive microstrain inside the nanocrystals became tensile in nature. Both the coercive field and saturation magnetization were reduced with increasing In3+ ion concentration in nickel–cobalt ferrite nanoparticles. Overall effective anisotropy was noticed to decrease with In3+ ion doping. This is due to the diamagnetic response of indium ions and weakening of magnetic interactions. Hopping of electrons between sublattice sites was the charge conduction process for all nanoferrites as confirmed by the AC conductivity measurement. Single semi-circular arc was observed in Cole–Cole plot for all samples which also revealed that the non-conductive grain boundaries was most effective in comparison to grains in dielectric responses. Decrement in the radius of semi-circles with respect to pristine sample also indicated the enhancement in DC conductivity with indium doping. [ABSTRACT FROM AUTHOR]

In this work, we report co-doping of two types of magnetic ions in ZnO nanoparticles with the generic formula TM TM ZnO (x = 0.025, 0.05 and 0.1), where TM indicates transition metal. X-ray diffraction studies confirms the phase purity of synthesized nanoparticles. All the samples show hexagonal wurzite crystal structure. No impurity peaks were observed within the X-ray diffraction limit. Spherical nanoparticles with uniform size ranging from 22 to 23 nm were observed using field emission scanning electron microscopy. Band gap ranging from 3.26 to 3.40 eV were calculated by using UV-Vis spectroscopy. Photoluminescence spectroscopy shows the presence of defect structures due to oxygen vacancies in the nanoparticles. Raman spectra confirm the crystallinity of the sample observed from the Raman mode at 437 cm. In Raman spectra, the broadening observed in the region 1,100-1,500 cm which was attributed to multiphonon modes which also confirmed the presence of defects in synthesized nanoparticles. All the co-doped samples show a paramagnetic behavior. Weak ferromagnetic behavior starts appearing for samples with x = 0.1. This ferromagnetism is attributed to the additional impurity phases in the sample. [ABSTRACT FROM AUTHOR]

Adsorption of 3-aminopropyltriethoxysilane (APTS) on magnetite nanoparticles during its formation has been investigated to optimise the preparation of stable aqueous dispersion of amine derivatised magnetite nanoparticles. APTS adsorbs chemically on the surface of magnetite particle modifying its surface which is evident from thermal and C, H, N analysis. The variation of particle size has been observed with change of APTS concentration. X-ray diffractogram shows the formation of pure inverse spinel phase magnetite with average crystallite size 7 nm when equimolar (Fe3O4: APTS = 1:1) quantity of APTS was used during its synthesis. The presence of free surface –NH2 groups and Fe–O–Si bonds was observed by FTIR. Raman spectrum further confirms the presence of surface –NH2 groups. Transmission electron microscopy shows formation of particles of average size between 7 nm and 12 nm. The effective hydrodynamic diameter of the APTS coated particle agglomerates is 45.8 nm in stable aqueous colloidal dispersion, which is evident from photon correlation spectroscopy. VSM measurements at room temperature of both silanised and unsilanised magnetite shows their superparamagnetic nature with saturation magnetisation 41 e.m.u/g and 56 e.m.u/g, respectively. Avidin has been immobilised on the surface through glutaraldehyde, which demonstrates the possibility of the synthesised material to be used in protein immobilisation to form bioactive magnetic particles. [ABSTRACT FROM AUTHOR]

Synthesis of core/shell structured ZnFe2O4/CuO nanoparticles with varying core diameter and different weight percentage of CuO phase [(1−x) ZnFe2O4/x CuO: x = 0.15, 0.30, 0.45 and 0.60] using double stage standard chemical co-precipitation method has been reported in this article. For first four samples only the diameter of core was varied and for other four samples only the weight percentage of CuO phase was varied. The existence of both cubic spinel ZnFe2O4 phase along with monoclinic CuO phase was verified by X-ray patterns recorded at room temperature. The average core diameter was in between 8 and 13 nm as estimated using Scherrer's formula and further verified by HRTEM images. A reduction in lattice parameter with increasing core thickness and also with increasing CuO phase was observed. A notable enhancement in coercivity and saturation magnetization were observed in field cooled (5 T) hysteresis loops obtained at 5 K for the first four varying core diameter core–shell structured nanoparticles in comparison to bare zinc ferrite nanoparticles of almost same size. A decreasing trend in coercivity and saturation magnetization was also noticed in low temperature hysteresis loops for higher CuO content samples. A considerable improvement in blocking temperature (TB) as well as Néel temperature (TN) for all the different core diameter samples were also found in M(T) protocols. Both blocking temperature and Néel temperature decreased for increasing CuO content in composite nanoparticles. The room temperature M(H) plots exhibited superparamagnetic nature with insignificant coercivity and negligible remanence. [ABSTRACT FROM AUTHOR]

We report the microstructural and magnetic characterization of single phase nanocrystalline partially inverted Zn 0.3 Ni 0.7 Fe 2 O 4 mixed spinel ferrite. The samples were annealed at 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. X-ray diffraction results indicate phase purity of all the samples and application of Debye- Scherrer yielded a crystallite size variation from 5 nm to 33 nm for the different samples. Magnetic measurements have revealed the freezing of interfacial spins which were the cause of the large horizontal M-H loop shift causing large exchange bias with high anisotropy. The magnetic measurements show a hysteresis loop with high effective anisotropy constant due to highly magnetically disordered surface spin at 5 K. [ABSTRACT FROM AUTHOR]

• Synthesis of single-phase ferrite nanoparticles. • Doping of Jahn-Teller active Cu2+ ions. • Lowering of crystal symmetry. • Observation of superparamagnetic behavior. • Good dielectric below 100 Hz. Samples with empirical formula Ni 1-x Cu x Fe 2 O 4 (x = 0.00, 0.25, 0.50, and 1.00) were prepared using chemical route. All the samples showed single spinel phase without any impurity. Average crystallite sizes were observed in the range of 12 nm to 39 nm as calculated by using Williamson-Hall (W-H) graphs. Raman spectra of all samples confirmed the lowering of crystal symmetry of octahedral sublattices with increasing Cu content. Signature of Jahn-Teller distortion due to substitution of Cu2+ (3d9) ions was detected using Raman spectroscopy. Absorption spectra of all the samples were recorded using UV–Vis spectroscopy, which confirmed the opaque character near red and infrared (IR) region. Onset of superparamagnetic behaviour has been observed by incorporating Cu2+ in the nickel ferrite with the mean blocking temperatures for all samples well below 300 K. Dielectric studies revealed that the grain boundaries played a major role in controlling the properties with increase in Cu2+ percentage. [ABSTRACT FROM AUTHOR]