Nanocrystalline Spinel Mn Cu Fe O Ferrites-Synthesis and Structural Elucidation Using X-Ray Diffraction and Positron Annihilation Techniques

• Published in: IEEE transactions on magnetics 2010-03, Vol.46 (3), p.847-851
• Main Authors: Predeep, P., Prasad, Arun S., Dolia, S. N., Dhawan, M. S., Das, D., Chaudhuri, S. K., Ghose, Vipasha
• Format: Article
• Language: English
• Subjects: Copper; Crystal structure; Ferrites; Ionic radii; Iron; Lattices; Magnetic materials; Magnetic properties; Magnetism; Manganese; nanocrystalline spinel ferrites; Physics; positron annihilation; Positrons; X-ray diffraction
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2009.2031109

We have synthesized a series of nanocrystalline ferrite samples with the composition Mn x Cu 1-x Fe 2 O 4 (x=0.2, 0.4, 0.6, 0.8) by an advanced sol-gel auto-combustion method. The X-ray diffraction patterns confirm the existence of single-phase cubic spinel crystal structure of ferrites with lattice parameter ranges from 8.395 ¿ to 8.45 ¿. We report the equilibrium radii for tetrahedral and octahedral sites in the unit cells and the estimated cation distribution over the two sites of nanocrystalline Mn x Cu 1-x Fe 2 O 4 . We also estimate the oxygen positional parameter as 0.389. The positron annihilation life time spectroscopic studies were carried out for all the samples and analyzed the variation of life time parameters ¿ 1 ; I 1 , ¿ 2 ; I 2 and the mean life time ¿ m to elucidate the defect structure of the nanocrystalline Mn x Cu 1-x Fe 2 O 4 . We found that the overall vacant type defects fill up as the Mn 2+ ion concentration, x, increases. The value of ¿ 1 varies from 150 ps to 170 ps and that of ¿ 2 varies from 295 ps to 335 ps, which are the characteristic values for nanocrystalline samples, indicating the presence of intergranular as well as surface-diffused vacancies in the crystal structure.