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

Abstract

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 Mössbauer 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 × 10(5) 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)(f) 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).

Raman spectra of Ni1‐XZnXFe2O4 nanopowders

“…For Fe 3 O 4 (structural analog of Ni 1‐x Zn x Fe 2 O 4 ferrites), for example, neutron, X‐ray diffraction studies, electron microscopy, and nuclear magnetic resonance, it was shown that the structure of the low‐temperature phase has the form of monoclinic supercell with symmetry group Cc. Similar examples can be cited …”

“…The latter brings about the variation of exchange spin oscillations in them that is experimentally confirmed by EPR investigations given in papers . We notice that the presence of lines referred to magnon oscillations is not good interpreted with two‐sublattice model of Ni 1‐x Zn x Fe 2 O 4 ferrites, magnetic space group of which published, for example, in Litvin and does not take in account the weak magnetic field of jumping 3d‐electrons . In order to explain them, it is more reasonable to use the model to take into account the magnetic ordering related to the presence of jumping 3d‐electrons, which forms the third weak magnetic sublattice.…”

“…Similar examples can be cited. [20][21][22][23] Changes in the valences of cations and their crystallographic positions between tetrahedral and octahedral sites of the spinel structure contribute to deviation from stoichiometry and the formation of defects. This can lead to localized and delocalized distortions, which accumulate mainly in the family of high-index planes of spinel structure.…”

Magnetic, electric and thermal properties of cobalt ferrite nanoparticles

“…The conductivity and Neel temperature dependence with grain size has been investigated in nanocrystalline cobalt ferrite powder for one composition only, namely CoFe 2 O 4 [19][20][23][24]. Most of the magnetic or electric investigations of nanoparticles of cobalt ferrites in literature concern Cd , Al or Zn doped ferrites [25][26][27]. Magnetic properties and transport mechanisms of cobalt ferrites Co x Fe 3-x O 4 with various compositions were studied [28], but in that case the grain sizes were in the micronic range.…”

Mössbauer Spectra and Crystallite Size Related Magnetic/Electric Properties of Yb Substituted Zn-Ferrite Nanoparticles

“…Values of QS of QS D1 = 0 33 mm/s and QS D2 = 0 40 mm/s obtained at 800 C are in agreement with the values observed for bulk sample. 8 At 300 K the magnetization M(H) curve for Zn0 and Zn300 shows nearly zero coercivity, 4 in agreement with the superparamagnetic behavior expected for these nanoparticles on the time scale of the magnetization measurement time M ∼ 100 s. Whereas for a typical dc magnetization measurement the M is ∼ 10 2 s, for Mössbauer spectroscopy the measuring time depends on the Larmor precession time L of the nuclear magnetic moments, with L = 10 −8 -10 −9 s in the case of 57 Fe nuclei. Accordingly, room temperature Mössbauer spectra for Zn0 show magnetic order.…”