Mössbauer Effect Study of Superparamagnetic Behavior of ZnFe₂O₄ Nanoparticles Formed in ZnO Doped with Fe₂O₃

Abstract

Superparamagnetic behavior of ZnFe2O4 nanoparticles formed by doping ZnO with various content of α‐Fe2O3 is investigated by 57Fe Mössbauer spectroscopy measurements performed in a temperature range from 300 to 10 K. The nanoparticles were obtained by the hydrothermal synthesis with Fe2O3 doping ranging from 30 to 70 wt.%. The results are compared with the ZnO sample doped with 60% Fe2O3, prepared by the calcination method. At room temperature the Mössbauer spectra of all samples consist of a nonmagnetic component characteristic for Fe3+ ions in ZnFe2O4 spinel structure. Low temperature Mössbauer measurements of hydrothermally synthesized nanoparticles reveal appearance of a magnetically ordered spectral component at about 120 K for the sample doped with 70% Fe2O3 and below 30 K for all other compositions. The spectral contribution of the magnetic component increases gradually at decreasing temperature at the expense of the nonmagnetic component, indicating superparamagnetic relaxation of ZnFe2O4 nanoparticles. It is concluded that the spinel nanoparticles are significantly smaller in the samples obtained by the hydrothermal method than by the calcination one. The blocking temperature is found to decrease with decreasing content of Fe2O3 doping during preparation of the nanoparticles.

Formation of Oriented Nanowires from Mixed Metal Oxides

“…The major contribution of the sextet Mössbauer components is characteristic of the presence of Fe 3 O 4 predominantly and α-Fe 2 O 3 in studied materials (Table 2) [22,23]. The presence of doublet patterns could be assigned to the contribution of Fe-bearing phases in non-stoichiometric Fe 1-x O and ZnFe 2 O 4 [24,25]. Table 3 shows the data estimated after the decomposition of Mössbauer spectra in the samples obtained using ps ablation.…”

Design and Catalytic Behaviour of Hosted in Activated Carbon Foam CoxZn1−xFe2O4 Ferrites

“…The doublets in the spectra possessed parameters of Fe 3+ ions (Figures S5 and S6, Table 3) and probably originate from the particles with a superparamagnetic behavior [72]. The higher quadruple splitting of the doublets than the reported ones for pure ZnFe 2 O 4 (∆ = 0.4 mm•s −1 ) [73,74] proposes the existence of small (below 10-12 nm) and highly defective ferrite particles [72]. This assumption was in agreement with the HRTEM results (Figure 5).…”

“…The observed decrease in the doublet part in the LNT spectrum as compared to the corresponding room temperature one evidences the presence of very small iron-containing particles (bellow 4 nm) with a supperparamagnetic behavior. The appearance of two sextets of iron ions in octahedral coordination (Table 3) indicates a different number of nearby neighbor iron ions from the tetrahedral sublattice [72].…”