Mild nitridation of perovskite manganite: Synthesis, structure and magnetism

Abstract

The nitrogen lightly doped perovskite manganite La0.5Ba0.5MnO(3-δ)-xNx was synthesized following a mild nitridation strategy by optimizing annealing temperature, annealing time and NH3/Ar flow rate ratio. Neutron powder diffraction (NPD) characterization evidences an N-doping triggered structural phase transition from pseudo-cubic Pm-3m to tetragonal P4/mmm and further confirms a preferable substitution at O1 and O2 sites closing to the Ba-rich layers. N 1s K-edge X-ray absorption near edge spectrum (XANES) with total fluorescence yield (TFY) mode, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy collectively convince the Mn–N bonded state. The O/N atomic ratio is determined to be 2.26/0.22 by XPS analysis closing to the value of 2.25/0.18 from NPD refinement. Magnetic property characterization reveals that both long-range Mn3+-O-Mn4+ ferromagnetic coupling and high Curie temperature (TC) are maintained upon N-doping. Besides, significant spin frozen with robust domain pinning is identified below TC which can be ascribed to the short-range Mn–N–Mn clusters and/or oxygen defects. This work expands the connotation of transition-metal based perovskite oxynitride and may inspire the development of photosensitive semiconductor device with magnetic response.