Investigation of Crystal Structure, Electrical and Magnetic Properties of Spinel Mn-Cd Ferrite Nanoparticles

The role of thermal treatment and formulation on modifying the structural nature and optimizing certain physical features of coprecipitated superparamagnetic Co-Mn-Cr spinel ferrite

Examining the composition and heat treatment effects of co-precipitated Co0.7Mn0.3CrxFe2-xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1) ferrite nanoparticles provides valuable insights into the structural, morphological, optical, magnetic, and electrical properties of these materials. X-ray diffraction (XRD) and Rietveld refinement analyses confirm the spinel cubic crystalline phase of the samples, indicating the formation of well-defined crystal structures. Transmission electron microscope micrographs manifest the nanoscale nature of the produced specimens and their narrow particle size distribution with a small standard deviation. This uniformity is often desirable in many applications because it confirms the similarity of the properties and behaviors of the nanoparticles. The Fourier transform infrared spectroscopy study suggests that the substitution of Cr3+ ions at octahedral sites influences molecular stability. Annealing causes a slight expansion in bond length and a subsequent decrease in stability. The presence of Cr3+ ions enhances the strength of the specimens, while annealing weakens them. This indicates a fine balance between composition and processing conditions in determining the strength of the materials. The estimated optical indirect bandgap undergoes a redshift by adding Cr3+ ions. Annealing at elevated temperatures reduces the bandgap due to the quantum confinement effect, indicating the tunability of optical properties through compositional and thermal control. Samples with x ≥ 0.6 exhibit nearly zero coercivity, indicating superparamagnetic behavior, which have promising applications. The preference of Cr3+ ions to occupy octahedral B-sites influences the magnetic behavior of the materials. The dielectric polarization and dielectric loss improved by adding Cr3+ ions, while the alternating current conductivity decreased. From impedance spectroscopy, the real and imaginary parts, Z' and Z", were increased by increasing Cr content. Furthermore, the annealing process greatly affects the electrical properties of the specimens. Overall, the study emphasizes the intricate relationship between composition, annealing conditions, and the resulting structural, magnetic, and electrical properties of Co-Mn-Cr ferrite nanoparticles, providing significant observations for the development of tailored materials for diverse applications in electronics, magnetics, and medicine.

Benchmark Crystal Structure of Defect-Free Spinel ZnFe2O4

Accurate structural models are of paramount importance for elucidating structure-property relationships in functional materials. Spinels (AB2O4) form a highly important family of materials with complex crystal structures, and subtle structural details have a critical bearing on understanding their physical properties. In some spinels, the space group symmetry is debated, and in general, point defects such as cation inversion and interstitials add complexity. Most studies of spinels concern powder materials, and this challenges deep structural characterization. In fact, most published spinel structures have dubious atomic displacement parameters (ADPs), which is a typical sign of problematic structural description in the refinement of diffraction data. Here, we use various X-ray and neutron diffraction techniques to establish a benchmark crystal structure for the essentially defect-free spinel ferrite ZnFe2O4, which is a widely studied frustrated magnet. It is shown that the appearance of Fd3̅m forbidden reflections in the ZnFe2O4 single-crystal neutron diffraction data is an artifact of multiple scattering rather than the loss of inversion symmetry. We then provide benchmark ADPs and demonstrate how strongly these parameters affect the refined cation inversion. The ADPs reported here may be used as reference data to test the soundness of refined structural models, possibly to constrain those based on suboptimal data quality, and thereby provide a more accurate fundamental understanding of the structure-property relationship in spinel-type materials.