Structural, dielectric, magnetic and optical properties of double perovskite oxide Sm <sub>2</sub> NiMnO <sub>6</sub> nanoparticles synthesized by a sol−gel process
Kai Leng, Weiren Xia, Qingkai Tang, Yang Li, Yuting Xie, Zhiwei Wu, Kang Yi, Xinhua Zhu
Abstract
Abstract Here we report on the structural, dielectric, magnetic and optical properties of double perovskite Sm 2 NiMnO 6 (SNMO) nanoparticles synthesized by a sol−gel method. Structural Reitveld refinements on x-ray powder diffraction data revealed that the SNMO nanoparticles crystallized in a monoclinic crystal structure with P 2 1 / n space group. SEM and (HR)TEM images revealed the phase purity and single-crystalline nature of the SNMO nanoparticles. XPS spectra confirmed the presence of Sm 3+ , Ni 2+ and Mn 4+ ions in the SNMO nanoparticles and oxygen in the forms of lattice oxygen and the hydroxyls species. SNMO ceramics exhibited relaxor-type dielectric behavior, well fitted by modified Curie−Weiss law. Such dielectric behavior originated from the interactions of random dipoles arisen from the B-site cations disorder accompanied with the variations in local electric fields and local strain fields due to the different radii of B-site cations, and/or the virtual electrons hopping between the Ni 2+ and Mn 4+ cations. Magnetic data demonstrate the variations of the magnetic transitions at low temperatures and the spin glass-like behavior below 11 K, which is attributed to the spin fluctuations induced by the competing interactions between the ferromagnetic (FM) and antiferromagnetic phases. Large positive Curie−Weiss temperature ( θ p ) indicates the dominant FM super-exchange interactions in the SNMO samples. The SNMO nanoparticles have a direct optical band gap of 1.42 eV, close to 1.34 eV in a single junction solar cell. That enables the SNMO nanoparticles to be useful for solar cell absorbers.