Structural, optical, dielectric and magnetic properties of CaFe2O4 nanocrystals prepared by solvothermal reflux method

Single crystalline CaFe2O4 nanospheres were synthesized by solvothermal reflux method using high boiling point organic solvents mixture. Both X-ray diffraction and electron diffraction profiles were confirmed single phase nature of the compound. The sample shown spherical morphology with average particle size of 10 nm which is same as crystallite size determined from the XRD. A thin layer of surfactant oleic acid was adsorbed on the surface of the nanoparticles. The optical excitation spectra reveals that the compound has direct allowed energy bandgap of 1.26 eV. The temperature dependent dielectric constant (epsilon '(r)) and dielectric loss (epsilon ''(r)) measurements show low values at room temperature and were nominally changes with enhance of temperature upto 650 K. Above which both epsilon '(r) and epsilon ''(r) were steeply increased with small variation of temperature which could be assigned to enhanced electrical conductivity due to surface charge conduction and, partially, to on-set of decomposition of oleic acid present on the surface of the sample. The samples show variable electron hopping conductivity in the temperature range studied and was supported by both Arrhenius plots and electric modulus studies at different frequencies. The CaFe2O4 nanoparticles show superparamagnetic nature at room temperature with high saturation magnetization (48.54 emu/g). The magnetization is much higher than ferrimagnetic bulk magnetization. Langevin function fit to magnetization data give 8 nm magnetic domain diameter and 1 nm magnetically disordered thin shell on the surface of the nanoparticles. As CaFe2O4 nanoparticles were electrically resistive and low dielectric loss materials, they may find applications in microwave engineering. In addition, the CaFe2O4 superparamagnetic nanoparticles were biocompatible and have high saturation magnetization, they could be used in biomedical applications such as magnetic hyperthermia and directed drug delivery applications. (C) 2017 Elsevier B.V. All rights reserved.