Magnetically frustrated calcium-substituted SrMn₂Fe₄O₁₁ R-type hexaferrite nanoparticles for biomedical applications

This research project was based on the idea of inducement of more magnetic frustration in already frustrated R-type hexagonal ferrite by the substitution of divalent ions to gain more magnetic disordering in the material and to evaluate the preliminary biomedical testing. So, the magnetic phase transition occurred, and the ferrimagnetic material turned into a superparamagnetic material upon substituting the divalent Ca²⁺ ions in pure Sr²⁺ based R-type hexagonal ferrites. Crystallographic X-ray diffraction data gave evidence that all the samples display the R-type hexagonal structure with space group P6₃/mmc. VSM study proves that with the substitution, the magnetic parameters decreased. Low temperature-dependent magnetic properties reveal the existence of short-range magnetic ordering among the substituted sample, and the blocking temperature (T _b) was measured from DC and AC magnetic data. The average particle sizes measured by TEM micrographs, and spherical-shaped particles were also calculated theoretically by using the Langevin function which matched the TEM results. The average particle sizes measured by TEM micrographs lay in the range from 8-17 nm respectively. Owing to the finite particle size of present synthesized samples, their low value of coercivity and their response to external applied magnetic fields, they become better candidates to be used for biomedical applications. Also, these nanoparticles are characterized to obtain their cytotoxicity, antibacterial activities, and biodistribution properties. The antibacterial analyses were performed on two bacteria Escherichia coli (E. coli), and Staphylococcus aureus (S. aureus) by agar well diffusion method, while the inhibition zone lies between the range from 15-30 mm. Cell viability testing has been performed on A549 cell lines by adopting the MTT assay method. The obtained results show that the Ca²⁺ substituted sample shows more cytotoxicity owing to small particle size as compared with the pure R-type hexagonal ferrite. To evaluate the route of radiolabelled NP's into the organs of rabbits the scintigraphy images were examined using a dual head SPECT gamma camera. The uptake counts are decreased over time in each organ with the maximum counts found in the bladder at the 4th hour owing to the gradual clearance of radiopharmaceuticals from the animal body.