Lawrence Kumar

Rietveld analysis of XRD patterns of different sizes of nanocrystalline cobalt ferrite

Nanocrystalline cobalt ferrite powder has been synthesised by citrate precursor and co-precipitation methods. Structural characterization of the samples has been carried out using powder X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscope (FE-SEM). Distribution of cations among the two interstitial sites (tetrahedral and octahedral sites) has been estimated by analysing the powder X-ray diffraction patterns by employing Rietveld refinement technique, and the results reveal the existence of samples as a mixed type spinel with cubic structure. It is observed that the distribution of cations and structural parameters are strongly dependent on synthesis method and annealing temperature. The vibrational modes of the octahedral and tetrahedral metal complex in the sample have been examined using FT-IR in the wave number range of 390 to 750 cm−1, and it shows an absorption band within this range, which confirms the spinel structure of the sample. The existence of constituents in the sample, i.e., Co, Fe and O has been authenticated using energy dispersive spectrum with the help of a FE-SEM.

Effect of Annealing Temperature and Preparation Condition on Magnetic Anisotropy in Nanocrystalline Cobalt Ferrite

Nanocrystalline cobalt ferrite (CoFe₂O₄) materials have been synthesized by citrate precursor and co-precipitation method. Samples are annealed at different temperatures to obtain the different nanocrystallite-size materials. All the samples crystallize to <i>Fd3̅m</i> space group in cubic symmetry. Magnetic hysteresis loops measurement has been carried out at room temperature using a vibrating sample magnetometer (VSM). The magnetic data in the saturation region have been analyzed by employing the law of approach (LA) to saturation technique. The anisotropy constant ( <i>K</i>₁) is found to be higher in citrate precursor derived samples. The saturation magnetization ( <i>M</i>_s), coercivity ( <i>H</i>_c) , remanent magnetization ( <i>M</i>_r) and anisotropy constant ( <i>K</i>₁) increases with the increase of crystallite size.

Effect of Ho3+ substitution on the cation distribution, crystal structure and magnetocrystalline anisotropy of nanocrystalline cobalt ferrite

Ho3+ ion-substituted nanocrystalline cobalt ferrite materials with the chemical formula CoFe2− x Ho x O4 for x = 0.0, 0.025, 0.05, 0.075 and 0.1 have been synthesised by standard citrate precursor method. Crystal structure and phase purity have been studied by powder X-ray diffraction (XRD) method by employing Rietveld refinement technique. The distribution of cations between the tetrahedral site (A-site) and octahedral site (B-site) has been estimated by Rietveld analysis. The refinement result shows that Ho3+ ion has a strong preference for octahedral sites (B-sites). The lattice constants decrease with the Ho3+ concentration up to x = 0.05. Crystallite size decreases with the Ho3+ concentration. The magnetic hysteresis loop measurements have been carried out at room temperature using a vibrating sample magnetometer (VSM) over a field range of ±2 T. The magnetisations in saturation have been analysed by employing the ‘law of approach (LA)’ technique. The magnetocrystalline anisotropy constant and saturation magnetisation are found to decrease with the Ho3+ concentration up to x = 0.05. The coercivity decreases with the Ho3+ concentration. The vibrational modes of the octahedral and tetrahedral metal complex in the sample have been carried out using Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra of the samples have been analysed in the wave number range of 350–1000 cm−1. We have observed two prominent absorption bands which are assigned to tetrahedral and octahedral metal complexes. The elemental analysis has been carried out using energy dispersive spectroscopy (EDS) with the help of field emission scanning electron microscope (FE-SEM) and the results reveal that, elements are as per the stoichiometric ratio in all the samples.