XRD, HRTEM, Raman and magnetic studies on chemically prepared nanocrystalline Fe-doped gadolinium oxide (Gd1.90Fe0.10O3−δ) annealed in vacuum

Abstract

Nanoparticles of Fe-doped gadolinium oxide (Gd_1.90Fe_0.10O_3−δ) are prepared by a co-precipitation method. To obtain the desired nanocrystalline phase and to enhance the oxygen vacancy, the as prepared sample is annealed at 700 °C for 6 h in vacuum. The pure crystallographic phase is confirmed by Rietveld analysis of the X-ray diffraction (XRD) pattern. High resolution transmission electron microscopy (HRTEM) studies and Raman spectroscopy of the doped sample observed at room temperature also ruled out the presence of any unwanted impurity phase in the sample. XRD, HRTEM and Raman spectra of the sample confirmed the complete substitution of Fe-ions in the lattice of gadolinium oxide. The static magnetic measurements are carried out at different temperatures from 300 K down to 5 K by using a superconducting quantum interference device (SQUID) magnetometer. The onset of nonlinearity in the magnetization (M) vs. field (H) curve recorded at ∼20 K confirms the presence of magnetic ordering at and below ∼20 K. A clear hysteresis loop with a high value of magnetization (∼120.1 emu g⁻¹) is observed at 5 K at an applied field of ∼5 T. The lack of saturation in the hysteresis loop at and below ∼20 K and good fitting of the M–T curve below ∼50 K by 3D spin wave model and Curie–Weiss law indicates the coexistence of paramagnetic (PM) and ferromagnetic (FM) phases. The observed magnetic phase transition is attributed to the substitution of Fe-ions in the Gd₂O₃ lattice, which is explained by oxygen vacancy mediated bound magnetic polaron model.