Magnetic and Mossbauer studies of pure and Ti-doped YFeO3 nanocrystalline particles prepared by mechanical milling and subsequent sintering

Single-phased nanocrystalline particles of pure and 10 % Ti4+-doped perovskiterelated YFeO3 were prepared via mechanosynthesis at 450 degrees C. This temperature is similar to 150-350 degrees 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 Ti4+ ions prefer interstitial octahedral sites in the orthorhombic crystal lattice rather than those originally occupied by the expelled Fe3+ ions. Magnetic measurements show canted antiferromagnetism in both types of nanoparticles. Doping with Ti4+ lowers the Neel temperature of the YFeO3 nanoparticles from similar to 586 K to similar to 521 K. The Ti4+-doped YFeO3 nanoparticles exhibit enhanced magnetization and coercivity but less magnetic hyperfine fields relative to the un-doped nanoparticles. The Fe-57 Mossbauer spectra show similar to 15 % of the YFeO3 nanoparticles and similar to 22 of Ti4+-doped YFeO3 ones to be superparamagnetic with blocking temperatures < 78 K. The broadened magnetic components in the Fe-57 Mossbauer spectra suggest size-dependent hyperfine magnetic fields at the Fe-57 nuclear sites and were associated with collective magnetic excitations. The Fe-57 Mossbauer spectra show the local environments of the Fe3+ ions in the superparamagnetic nanoparticles to be more sensitive to the presence of the Ti4+ ions relative to those in the larger magnetic nanoparticles.