Effects of an external magnetic field on the hyperfine parameters in RE2O3 (RE = Gd, Er) nanoparticles measured by perturbed angular correlation spectroscopy

Abstract

The RE2O3 (RE = rare-earth) oxides present three different structures depending on the RE ionic radii: hexagonal (A-type), monoclinic (B-type) or cubic (C-type). In the latter, RE ions occupy two non-equivalent cation sites: asymmetric 24d sites and symmetric 8b sites. Gd2O3 and Er2O3 crystallize in this structure and have a paramagnetic behavior, although Er2O3 also orders antiferromagnetically below 4 K. Due to the high magnetic moment of Gadolinium ions, Gd3+ chelates have been used as a contrast agent for magnetic resonance imaging[1]. An investigation of the localized magnetic moment behavior on Gd and Er sites in Gd2O3 and Er2O3 nanoparticles (NPs), within an atomic resolution, under the influence of an external magnetic field (EMF), is very necessary mainly because the high neutron absorption cross-section of Gd prevents the use of neutron diffraction[ 2]. In this paper, hyperfine interactions, measured by Perturbed Angular Correlation (PAC) spectroscopy using 111In→111Cd as probe nuclei, were used to investigate the behavior of each RE site in Gd2O3 and Er2O3 NPs with and without the application of an EMF of 0.5 T. NPs were synthesized by thermal decomposition and characterized by transmission electron microscopy and X-ray diffraction. Results show that the contribution of RE atoms at 24d sites is invariant with temperature whereas the contribution from RE atoms at 8b sites is so that the hyperfine magnetic field (Bhf) increases in Er2O3 and decreases in Gd2O3 when temperature decreases indicating an opposite alignment of Gd magnetic moments at the 8b symmetric sites.