Influence of Particle Size on the Electrical Properties and Magnetic Field Dependent I–V Characteristics of Nanocrystalline ZnFe2O4
28 Jun 2019-Transactions of The Indian Ceramic Society (Taylor & Francis)-Vol. 78, Iss: 2, pp 111-120
TL;DR: The influence of grain size (7-16 nm) on electrical conductivity, dielectric properties and magnetic field dependent I-V characteristics along with magnetoresistance have been studied for zinc ferr... as discussed by the authors.
Abstract: The influence of grain size (7-16 nm) on electrical conductivity, dielectric properties and magnetic field dependent I–V characteristics along with magnetoresistance have been studied for zinc ferr...
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Abstract: Four powder samples of Nickel ferrite (NiFe2O4) with different morphology and nanoparticle size have been synthesized by various methods: electrospinning, hydrothermal, green, and sol-gel. Through the use of XRD, FT-IR, SEM, TEM, and BET techniques, the prepared powders were characterized. The produced ferrite displayed a cubic spinel phase with various nanofiber, nanotube, nanorod, and nanosphere morphological structures. The electrical conductivity values for each sample increased with increasing temperature indicating the semiconducting behavior of all samples. The conductivity values were found to be dependent on each nanoparticle's size and morphology. The variation of dielectric constant (ε′), dielectric loss (ε′′), and ac conductivity for the investigated samples at different temperatures and frequencies has been studied. Both dielectric constant (ε′) and dielectric loss (ε′′) were decreased with the increase of frequency while A.C. conductivity increased. Knop's phenomenological theory explains the frequency variation of (ε′ and ε′′). The hopping of electrons and holes is suggested to be the electrical conduction mechanism.
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TL;DR: In this paper, the average grain size and the root mean square strain were estimated from the x-ray diffraction line broadening, and the lattice parameter initially decreases slightly with milling and it increases with further milling.
Abstract: Nanostructured ZnFe2O4 ferrites with different grain sizes were prepared by high energy ball milling for various milling times. Both the average grain size and the root mean square strain were estimated from the x-ray diffraction line broadening. The lattice parameter initially decreases slightly with milling and it increases with further milling. The magnetization is found to increase as the grain size decreases and its large value is attributed to the cation inversion associated with grain size reduction. The Fe-57 Mossbauer spectra were recorded at 300 K and 77 K for the samples with grain sizes of 22 and 11 nm. There is no evidence for the presence of the Fe2+ charge state. At 77 K the Mossbauer spectra consist of a magnetically ordered component along with a doublet due to the superparamagnetic behaviour of small crystalline grains with the superparamagnetic component decreasing with grain size reduction. At 4.2 K the sample with 11 nm grain size displays a magnetically blocked state as revealed by the Mossbauer spectrum. The Mossbauer spectrum of this sample recorded at 10 K in an external magnetic field of 6 T applied parallel to the direction of gamma rays clearly shows ferrimagnetic ordering of the sample. Also, the sample exhibits spin canting with a large canting angle, maybe due to a spin-glass-like surface layer or grain boundary anisotropies in the material.
339 citations
TL;DR: From measurements of resistivity, activation energy, and Seebeck effect, an energy-level scheme is derived by which the semi-conducting properties of CoFe2O4 can be described as discussed by the authors.
297 citations
TL;DR: In this paper, the effect of the grain boundary effect on dc ionic conductivity was studied for ceria ceramics doped with trivalent dopants (Y3+, Gd3+, and La3+).
Abstract: The “grain-boundary effect,” which leads to a greatly reduced dc ionic conductivity due to the presence of a blocking layer in the vicinity of the grain boundaries, is studied in detail for ceria ceramics doped with various trivalent dopants (particularly Y3+, Gd3+, and La3+). The effects of porosity, of sintering time, and of dopant size and dopant concentration are investigated. Finally, it is shown that the grain-boundary effect virtually disappears when nearly silicon-free starting materials are used.
288 citations
TL;DR: The magnetic properties of the ball-milled sample are similar to those of ferrimagnetic MgFe2O4 powders having comparable grain size and inversion parameters as mentioned in this paper.
Abstract: Fine powders of ZnFe2O4 with an average particle size of 10 nm and inversion parameter of 0.21 were synthesized by the aerogel procedure. Portions of the powders were calcined in air at 500 and 800 °C and other portions were ball-milled for 10 h. The materials were characterized by x-ray diffractometry, vibrating sample, and SQUID magnetometry, Mossbauer spectrometry, and low temperature calorimetry. Upon calcination the powders underwent significant changes in grain size, inversion parameter, and hence magnetic properties. The magnetic state of the as-produced and calcined samples is best described as disordered and highly dependent on temperature. Upon ball-milling the grain size varied widely and the inversion parameter attained a value of 0.55. The magnetic properties of the ball-milled sample are similar to those of ferrimagnetic MgFe2O4 powders having comparable grain size and inversion parameters.
259 citations
TL;DR: In this article, stable colloidal aqueous suspensions of magnetic nanostructures made of copper, nickel, and zinc ferrites are reported, which could represent a new alternative for biological applications.
Abstract: We report on stable colloidal aqueous suspensions of magnetic nanostructures made of copper, nickel, and zinc ferrites. These magnetic fluids could represent a new alternative for biological applications. The basic steps of the nanoparticles synthesis, their chemical surface treatment, and their peptization in a stable colloidal sol are given. Their chemical composition is carefully checked, and X-ray diffraction patterns provide both their mean size and a structural characterization. Magnetization results obtained at 300 K are presented and discussed.
244 citations