Sr2Mn0.5Hf1.5O6-δ double perovskite oxides: Structural, dielectric, magnetic, optical and transport properties

Abstract

Double perovskite (DP) oxides with a chemical formula of A2B′B”O6 exhibit intriguing physical properties and structural flexibilities, which are widely used as a host structure to explore the novel candidates of half-metallic ferro-/ferrimagnetic materials. In this work, we have synthesized ferromagnetic Sr2Mn0.5Hf1.5O6-δ (SMHO) DP powders via solid-state reaction method. The powders had a magnetic Curie temperature up to 600 K, saturation magnetization of 0.59 emu/g at 2 K, and magnetic coercive field of 450 Oe. The SMHO ceramics displayed a butterfly-like magnetoresistance (MR)-H curve at 2 K due to the intergranular tunneling effect, and the MR (2 K, 7 T) value was −2.8 %. Structural investigations demonstrated the SMHO powders crystallized in an orthogonal crystal structure with Pnma symmetry. SEM images displayed a spherical morphology of the SMHO powders with particle size distribution of 100–200 nm. Quantitative EDS (energy dispersive X-ray spectra) data give out the percentage of Sr, Mn, Hf and O elements presented in approximately stoichiometric proportion. XPS spectra results confirmed the existence of Sr2+, Mn4+, and Hf4+/Hfx+(x＜4) ions in the powders, and oxygen elements were presented as the lattice oxygen and adsorbed oxygen species, respectively. Resistivity of the SMHO ceramics decreased continuously as the temperature increased from 2 K to 800 K, exhibiting a semiconductor behavior. The electrical transport data were well fitted by thermal activation model, small polaron hopping model, and Mott’s variable range hopping model, respectively in different temperature regions. Optical measurements gave out an indirect bandgap of 2.12 eV for the SMHO powders. Our present work demonstrates that the SMHO oxides are attractive in high temperature spintronic devices and solar cells owing to the integration of high TC, significant negative MR and optical bandgap located in the visible light window.