Investigation of positron annihilation lifetime and magnetic properties of Co1−xCuxFe2O4 nanoparticles

Abstract

Copper substituted cobalt ferrite nanoparticles, Co1−xCuxFe2O4 (x = 0, 0.25, 0.5, 0.75, 1.0) were effectively synthesized by employing co-precipitation procedure. The structural and magnetic properties of nanoparticles were examined through x-ray diffraction (XRD) technique, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and vibrating sample magnetometer (VSM). The cation distribution and lattice constant of samples are deduced from XRD patterns employing the MAUD program. Crystallite size of samples calculated with Scherrer formula showed all of samples are nanocrystallite. Distribution of vacancies in these compounds are studied using positron annihilation lifetime spectroscopy (PALS). The results of PALS measurements exhibited that by increasing the amount of copper substitution in cobalt ferrite, the vacancy dimensions are reduced until 0.5 and increased for 0.75 and again decrease for x = 1.0. Also, the number of vacancies in samples are without change, except for Cu = 0.5 and 1.0 that increased. Magnetic measurements showed that the value of the saturation magnetization (Ms) in the Co1−xCuxFe2O4 nanoparticles is negatively correlated with Cu substitution value, meaning the Ms decreases in a gradual way by increase in Cu substitution. Moreover, the coercivity of samples reduced with the increase in Cu ion substitution until Cu = 0.5, while for Cu = 0.75 coercive force enhanced and for Cu = 1.0 decreased again which this variation is similar to variation of the size of vacancies obtained with PALS. Therefore, the variation of vacancy size affects the coercivity of samples. The FTIR spectra of the prepared ferrite nanoparticles confirmed the presence of absorption bands in 410–600 cm−1 region which are assigned to tetrahedral and octahedral sites. These absorption bands increased with increase in copper content.