Experimental and theoretical investigation of structural, magnetic and optical properties of Nd2FeCrO6 and Gd2FeCrO6 perovskites synthesized by sol-gel technique

Abstract

In this investigation the physical properties of Nd2FeCrO6 and Gd2FeCrO6 double perovskites were studied both theoretically and experimentally. The first-principles predictions on the structural stability, magnetic behaviour and electronic structure of B-site ordered double perovskite Nd2FeCrO6 have been reported. The thermodynamic, mechanical, and dynamic stability analyses suggest the possibility of the synthesis of Nd2FeCrO6 double perovskite at ambient pressure. This compound shows ferrimagnetic (FiM) nature with 2 µB net magnetic moment and the magnetic ordering temperature has been estimated to be ∼265 K. Electronic structure indicates a higher probability of direct photon transition over the indirect transition with a band gap of ∼1.85 eV. Based on the theoretical prediction, Nd2FeCrO6 and Gd2FeCrO6 nanoparticles were synthesized for the first time using a facile citrate-based sol-gel method, and their structural, magnetic, and optical characteristics were thoroughly studied. Rietveld refinement analysis of the powder X-ray diffraction pattern of the synthesized Nd2FeCrO6 and Gd2FeCrO6 nanoparticles confirmed their single-phase orthorhombic and monoclinic structure with Pnma and P21/n space group, respectively. X-ray photoelectron spectroscopy confirmed the presence of mixed-valence states of Fe and Cr. The temperature dependent magnetization curves exhibited magnetic reversal behavior in Nd2FeCrO6 double perovskite at temperature 6 K in the field cooled (FC) mode. Interestingly, exchange bias effect was observed in this double perovskite material while the sample was cooled down from 300 K to 10 K and magnetic fields were applied during cooling. The zero-field cooled (ZFC) and field cooled curves of Gd2FeCrO6 perovskite largely diverged below 20 K. A downturn was observed in the ZFC curve at 15 K which corresponds to an antiferromagnetic, Néel transition. The narrow magnetic hysteresis loop of Gd2FeCrO6 recorded at 5 K was nearly saturated and demonstrated an asymmetric shift along the magnetic field axis indicating the concurrence of ferromagnetic and antiferromagnetic domains in Gd2FeCrO6 nanoparticles. The optical band gap of Nd2FeCrO6 and Gd2FeCrO6 nanoparticles are found to be 1.95 eV and 2.00 eV, respectively, evaluated experimentally from the UV–visible and photoluminescence spectroscopic analyses. Here, by employing experimentally obtained structural parameters of Gd2FeCrO6 perovskite in first-principles calculation, the spin-polarized electronic band structure, density of states and optical absorption property of Gd2FeCrO6 double perovskite were also investigated and compared the results with experimental outcomes. Therefore, due to the lower band gap and magnetically tunable exchange bias, it is anticipated that the newly synthesized Nd2FeCrO6 and Gd2FeCrO6 double perovskites could be the promising materials for visible-light-driven energy device and spintronic applications.