Structural, Optical, Magnetic, and Dielectric Properties of Cr3+ Substituted Cobalt Aluminate Nanoparticles

• Published in: Journal of superconductivity and novel magnetism 2019-07, Vol.32 (7), p.2119-2132
• Main Authors: El-Said Bakeer, D., Sakr, Abdel-Hamed
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Magnetic Materials; Magnetism; Original Paper; Physics; Physics and Astronomy; Strongly Correlated Systems; Superconductivity
• ISSN: 1557-1939; 1557-1947
• DOI: 10.1007/s10948-018-4931-1

The present study investigates the influence of Cr 3+ substitution on structural, optical, dielectric, and magnetic properties of cobalt aluminates in the aluminates series CoAl 2- x Cr x O 4 , 0.00 ≤  x  ≤ 0.20. These series of nanoparticles are effectively synthesized using the co-precipitation method. The cubic spinel aluminate structure is confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic measurements. Transmission electron microscopy (TEM) analysis shows the formation of spherical nanoparticles, which are homogeneous in shape and size. The optical properties of the prepared samples have been investigated by means of optical absorbance spectra. The optical band gap E opt i and Urbach energy E u are estimated. At room temperature, the magnetization of undoped CoAl 2 O 4 reveals a weak ferromagnetic behavior. This ferromagnetism is increased for the sample with x  = 0.05, and the samples with higher Cr 3+ content have a tendency to be superparamagnetic on account of the formation of single-domain particles as a consequence of small particle size. Real part of dielectric constant (ε ′ ), dielectric loss (tanδ), ac conductivity (σ ac ), real part of impedance ( Z ′ ), and imaginary part of impedance ( Z ″ ) are analyzed as a function of frequency and Cr 3+ content. The results show that the dielectric loss (tanδ), dielectric permittivity (ε ′ ), and ac conductivity (σ ac ) decrease with the increase in Cr 3+ content, x  = 0.05, and then increase with a further increase in Cr 3+ content. The increase in these parameters has been explained on the basis of the hopping mechanism. From the Cole–Cole diagram, the value of the relaxation time τ can be calculated and it has been found to increase with increasing the Cr 3+ content. Actually, a high dielectric constant makes these materials good for energy storage at high frequencies.