Ferrimagnetism and spin canting of Zn⁵⁷Fe₂O₄nanoparticles embedded in ZnO matrix

The structural and magnetic properties of ZnFe 2 O 4 nanoparticles embedded in a nonmagnetic ZnO matrix are presented. X-ray diffractograms and transmission electron microscopy images showed that the resulting samples are composed of crystalline ferrite nanoparticles with average crystallite size ⟨ D ⟩ = 23.4 ± 0.9 nm, uniformly dispersed within the ZnO matrix. Magnetization data indicated a superparamagnetic-like behaviour from room temperature down to T M ∼ 20 K, where a transition to a frozen state is observed. The M ( H ) curves displayed nearly zero coercive field down to T M , where a sharp increase in the H C value is observed. The measured saturation magnetization M S values at 200 and 2 K were M S = 0.028(3) and 0.134(7) μ B /f.u. ZnFe 2 O 4 , respectively, showing the existence of small amounts of non-compensated atomic moments. Mössbauer measurements at low temperatures confirmed the transition to a magnetically ordered state for T < 25 K, where two magnetically split sextets develop. Whereas these two sextets show strong overlap due to the similar hyperfine fields, in-field Mössbauer spectra clearly showed two different Fe 3+ sites, demonstrating that the sample is ferrimagnetically ordered. The two spinel sites are found to behave differently under an external field of 12 T: whereas the moments located at A sites show a perfect alignment with the external field, spins at B sites are canted by an angle α B = 49 ° ± 2 ° . We discuss the significance of this particle structure for the observed magnetic behaviour.