Temperature-Dependent Magnetic Response of Antiferromagnetic Doping in Cobalt Ferrite Nanostructures
In this work MnxCo1−xFe2O4 nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400–4000 cm−1 which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe2O4) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field.
Structural characterization and antistructure modeling of cobalt-substituted zinc ferrites
Abstract The cation distribution of the spinel system Zn1-xCoxFe2O4 (with x = 0; 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 0.9; 1.0) has been investigated by means of X-ray diffraction (XRD), Mossbauer spectroscopy and Fourier transform infrared spectroscopy (FTIR). In the present work, ferrites were prepared by co-precipitation method. XRD diffraction patterns show that all compositions have a pure single-phase cubic spinel structure over the whole composition range. It is found that both the lattice parameter and the average crystallite size decrease with increasing Co2+ content; from 8.4392 to 8.3536 A and from 37 to 25 nm for ZnFe2O4 and CoFe2O4, respectively. Morphological observations (SEM, TEM) reveal that the crystallinity decreases significantly with increasing Co2+ content meanwhile the particle size becomes more uniform. The elemental compositional stoichiometry have been carried out by means of energy dispersive analysis (EDS). The force constants Kt and Ko for the two sites have been deduced from IR band frequencies and compared with the trend of bond lengths: KT increases (from 2.084 to 2.144 dyn/cm2) because the bond length MA-O decreases, while KO decreases (from 1.043 to 0.948 dyn/cm2) because the bond length MB-O increases with increasing Co2+ content. For the first time antistructural modeling of zinc-cobalt ferrites considered. It shown that the acceptor in crystall latice is tetrahedral iron FeA , while the donor is octahedral cobalt Сo B ′ . With increasing Co2+ content, the concentration of active centers in tetrahedral and octahedral sublattice of zinc-cobalt ferrites are increases. The nature of the active centers are affecting on the chemical, electrical, magnetic, optical and catalytic properties of ferrites.
The Role of Cation Vacancy in Magnetic Annealing of Iron-Cobalt Ferrites
The kinetics of magnetic annealing effects in iron-cobalt ferrites is studied, based on a vacancy migration mechanism. First, a formal theory is developed, which makes clear the existence of a distribution of relaxation times in the phenomena. In order to get the distribution function of the relaxation time as a function of vacancy concentration and diffusion constants, a calculation based on a rather stochastic approach has been given. It is assumed that the dispersion in the relaxation time comes principally from the time required for the vacancies to migrate throughout the entire crystal lattice. The distribution function obtained is f(τ) = Wρτ/τ0×exp(−Wρτ/τ0), where ρ is the density of vacancies, τ0 is the mean relaxation time for the migration of a single vacancy, and W is a constant which depends on the lattice type, degree of short range ordering, and so on. On using this function the formation and the annihilation of the degree of directionality Su is expressed as ΔSu = ∫0∞f(τ)ΔS(τ)d(logτ), ΔS(τ) ...