Magnetic and Mössbauer studies of pure and Ti-doped YFeO ₃ nanocrystalline particles prepared by mechanical milling and subsequent sintering

Single-phased nanocrystalline particles of pure and 10 % Ti ⁴⁺-doped perovskite-related YFeO ₃were prepared via mechanosynthesis at 450^∘C. This temperature is ∼150–350 ^∘C lower than those at which the materials, in bulk form, are normally prepared. Rietveld refinements of the X-ray diffraction patterns reveal that the dopant Ti ⁴⁺ ions prefer interstitial octahedral sites in the orthorhombic crystal lattice rather than those originally occupied by the expelled Fe ³⁺ ions. Magnetic measurements show canted antiferromagnetism in both types of nanoparticles. Doping with Ti ⁴⁺ lowers the Néel temperature of the YFeO ₃ nanoparticles from ∼ 586 K to ∼ 521 K. The Ti ⁴⁺-doped YFeO ₃ nanoparticles exhibit enhanced magnetization and coercivity but less magnetic hyperfine fields relative to the un-doped nanoparticles. The ⁵⁷Fe Mössbauer spectra show ∼ 15 % of the YFeO ₃ nanoparticles and ∼22 of Ti ⁴⁺-doped YFeO ₃ ones to be superparamagnetic with blocking temperatures < 78 K. The broadened magnetic components in the ⁵⁷Fe Mössbauer spectra suggest size-dependent hyperfine magnetic fields at the ⁵⁷Fe nuclear sites and were associated with collective magnetic excitations. The ⁵⁷Fe Mössbauer spectra show the local environments of the Fe ³⁺ ions in the superparamagnetic nanoparticles to be more sensitive to the presence of the Ti ⁴⁺ ions relative to those in the larger magnetic nanoparticles.