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The magnetic behaviour of nanocrystalline ferrite is compared with the diluted dispersion systems containing 10–40 wt-% nickel ferrite in a polyethylene matrix. The zero field cooled (ZFC)/field cooled (FC) magnetic measurements [M(T)] and M(H) measurements suggest strong evidence of interparticle interaction (dipolar surface interactions) which cannot be ignored even in 10 wt-% nickel ferrite–polyethylene diluted system. The general magnetic behaviour of diluted dispersion is similar to that of the undiluted nickel ferrite. However, coercivity, remanence and saturation magnetisation are altered. The changes in the magnetic data are discussed in terms of magnetisation interactions that encourage flux closure configuration. [ABSTRACT FROM AUTHOR]

Abstract: In the previous papers [R.D.K. Misra, A. Kale, R.S. Srivatsava, O. Senkov, Mater. Sci. Technol. 19 (2003) 826; R.D.K. Misra, A. Kale, B. Hooi, J.Th. DeHosson, Mater. Sci. Technol. 19 (2003) 1617; A. Kale, S. Gubbala, R.D.K. Misra, J. Magn. Magn. Mater. 277 (2004) 350; S. Gubbala, H. Nathani, K. Koizol, R.D.K. Misra, Phys. B 348 (2004) 317; R.D.K. Misra, S. Gubbala, A. Kale, W.F. Egelhoff, Mater. Sci. Eng. B. 111 (2004) 164], we reported the synthesis, structural characterization and magnetic behavior of nanocrystalline ferrites of inverse and mixed spinel structure made by reverse micelle technique that enabled a narrow particle size distribution to be obtained. In the present paper, the reverse micelle approach has been extended to synthesize nanocrystalline ferrites with varying surface roughness of 8–18Å (the surface roughness was measured by atomic force microscopy) and the magnetic behavior studied by SQUID magnetometer. Two different kinds of measurement were performed: (a) zero-field cooling (ZFC) and field cooling (FC) magnetization versus temperature measurements and (b) magnetization as a function of applied field. The analysis of magnetic measurement suggests significant influence of surface roughness of particles on the magnetic behavior. While the superparamagnetic behavior is retained by the nanocrystalline ferrites of different surface roughness at 300K, the hysteresis loop at 2K becomes non-squared and the coercivity increases with increase in surface roughness. This behavior is discussed in terms of broken bonds and degree of surface spin disorder. [Copyright &y& Elsevier]

Nanocrystalline nickel, zinc and manganese ferrites synthesized by reverse micelle synthesis technique were characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction techniques, and the magnetic behavior studied by Superconducting Quantum Interference Device (SQUID). The three ferrites exhibit blocking temperatures of 16, 20, and 35 K, respectively. The difference in the blocking temperatures was attributed to the magnetocrystalline anisotropy and L–S coupling. The saturation magnetization of the three ferrites at 300 K was 25, 8, and 6 emu/g, respectively and at 2 K was 35, 17, and 15 K, respectively. The lower saturation magnetization in the case of nickel and manganese ferrite compared to their bulk counterparts is attributed to a core-shell like particle morphology. The increase in the saturation magnetization in the case of zinc ferrite nanoparticles is attributed to the change in the cation distribution from a normal spinel to a mixed spinel structure in the nanocrystalline form. [Copyright &y& Elsevier]