To Thanh Loan

Cation distribution in CuFe2O4 nanoparticles: Effects of Ni doping on magnetic properties

The Cu1−xNixFe2O4 nanoparticles (with x = 0, 0.3, 0.5, 0.7, and 1) were synthesized by using spray co-precipitation method at annealing temperature Ta = 900 °C in air for 5 h. The crystal structure, microstructure, oxidation state, and magnetic properties of the samples were characterized by using X-ray diffraction, synchrotron X-ray diffraction, scanning electron microscopy, X-ray absorption spectroscopy, and vibrating sample magnetometer. It was shown that all the samples have cubic structure. Lattice constant and grain size decrease, while the Curie temperature TC increases with increasing of Ni2+ content. A small amount of Fe2+ was found in all the samples. Cation distribution was determined by using a combination of magnetization measurements, extended X-ray absorption fine structure analysis, and Rietveld refinement from synchrotron X-ray diffraction data. It was indicated that Ni2+ ions occupy in octahedral site only, while Cu2+ ions distribute in both tetrahedral and octahedral sites. The variatio...

Single Phase Formation, Cation Distribution, and Magnetic Characterization of Coprecipitated Nickel-Zinc Ferrites

X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry were used to investigate the structural, morphological, and magnetic properties of Ni1-xZnxFe2O4 nanosubmicron powders (x = 0–0.8). The samples were prepared by a coprecipitation method at temperatures between 600 and 1100 degree Celsius for five hours. The lattice constant, average size of coherent scattering regions, and cation distribution were analyzed by Rietveld refinement of the X-ray diffraction measurements. Scanning electron micrographs showed that the particle size increased from the nano- to the submicron scale as the zinc content increased from x = 0 to x = 0.8. The magnetization as functions of temperature and applied magnetic field were measured on the single-phase samples obtained at an annealing temperature of 1100 degrees Celsius. The derived saturation magnetization and Curie temperature were compared to those of the bulk counterparts reported previously and discussed based on finite-size effects and possible nonmagnetic impurities. The influence of zinc substitution on the magnetic exchange interactions were studied based on molecular-field theory for compositions of 0 ≤x ≤ 0.4.

Synchrotron and Magnetic Study of Chromium-Substituted Nickel Ferrites Prepared by Using Sol-Gel Route

Structural and magnetic properties of NiCrxFe2-xO4(x = 0.7 and 0.9) spinel ferrites prepared by sol-gel route have been investigated using synchrotron X-ray powder diffraction (SXPD) and magnetization measurements. The gel products after annealing at 1000 °C for 2 h are found to crystallize in cubic phase. Rietveld refinements of X-ray diffraction and SXPD patterns revealed that the compounds are almost perfect inverse spinel with only few percents of nickel atoms located at the tetrahedral sites. Transmission electron microscopy (TEM) images showed that the samples are composed of nanoparticles with mean diameter in agreement with crystallite size determined by the Rietveld analysis. The spontaneous magnetization Ms as a function of temperature was determined via magnetization curves measured using vibrating sample magnetometer in a temperature range from 88 K to above Curie temperature in applied fields up to 10 kOe. The sample x = 0.9 shows a cancellation of sublattice magnetizations at 400 K. The temperature dependence of saturation magnetization Ms of the samples can be described in terms of molecular-field model for collinear spins with the derived cation distributions.