An integrated study of thermal treatment effects on the microstructure and magnetic properties of Zn-ferrite nanoparticles

Journal Article · Wed Sep 30 00:00:00 EDT 2015 · J. Phys. Condens. Matter

DOI:https://doi.org/10.1088/0953-8984/25/8/086001· OSTI ID:1222035

Antic, Bratislav ^[1]; Perovic, Marija ^[1]; Kremenovic, Aleksandar ^[1]; Blanusa, Jovan ^[1]; Spasojevic, Vojislav ^[1]; Vulic, Predrag ^[1]; Bessais, Lotfi ^[2]; Bozin, Emil S ^[3]

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1. Univ. of Belgrade (Serbia)
2. Univ. of Paris (France)
3. Brookhaven National Lab. (BNL), Upton, NY (United States)

The evolution of the magnetic state, crystal structure and microstructure parameters of nanocrystalline zinc–ferrite, tuned by thermal annealing of ~4 nm nanoparticles, was systematically studied by complementary characterization methods. Structural analysis of neutron and synchrotron x-ray radiation data revealed a mixed cation distribution in the nanoparticle samples, with the degree of inversion systematically decreasing from 0.25 in an as-prepared nanocrystalline sample to a non-inverted spinel structure with a normal cation distribution in the bulk counterpart. The results of DC magnetization and Mossbauer spectroscopy experiments indicated a superparamagnetic relaxation in ~4 nm nanoparticles, albeit with different freezing temperatures T_f of 27.5 K and 46 K, respectively. The quadrupole splitting parameter decreases with the annealing temperature due to cation redistribution between the tetrahedral and octahedral sites of the spinel structure and the associated defects. DC magnetization measurements indicated the existence of significant interparticle interactions among nanoparticles (‘superspins’). Additional confirmation for the presence of interparticle interactions was found from the fit of the T_f(H) dependence to the AT line, from which a value of the anisotropy constant of K_eff = 5.6 × 10⁵ erg cm^-3 was deduced. Further evidence for strong interparticle interactions was found from AC susceptibility measurements, where the frequency dependence of the freezing temperature T_f(ƒ) was satisfactory described by both Vogel–Fulcher and dynamic scaling theory, both applicable for interacting systems. The parameters obtained from these fits suggest collective freezing of magnetic moments at T_f .

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 1222035
• Journal Information: J. Phys. Condens. Matter, Vol. 25, Issue 8
• Country of Publication: United States
• Language: ENGLISH