Influence of Copper on Structure, Magnetic Properties, and Magnetic Induction Heating Response in Co–Cu Nanoferrites

Abstract

The study explores the exciting development of nanoferrite systems designed for magnetic hyperthermia applications. Nanoparticles with the formula Co_1-xCu_xFe₂O₄ (x = 0.00–0.20 in increments of 0.04) were synthesized through the sol–gel method, utilizing polyvinyl alcohol as a chelating agent to facilitate precise control over particle size. The as-prepared powders were annealed at 400 ℃, 600 ℃, and 800 ℃ to examine the influence of annealing temperature on the development of domains and size-dependent magnetic properties. Structural analysis using X-ray diffraction and transmission electron microscopy revealed well-crystalline spinel structures, with particle sizes ranging from 5.6 to 8 nm for samples annealed at 600 ℃, consistent with the crystallite sizes (from 5.5 to 8 nm) estimated from Williamson-Hall plots. At room temperature, the specific magnetization of pristine cobalt ferrite, measured under a maximum applied magnetic field of 20 kOe, showed a significant increase from 10 emu/g to 69.1 emu/g with the increase in annealing temperature from 400 to 800 ℃. The observed increase in coercivity (H_c) with annealing up to 600 ℃ is linked to crystal growth within the single domain region, whereas the subsequent decrease in H_c at 800 ℃ is associated with the transition of particles to a multidomain state. The single domain nanoparticles, prepared by annealing at 400 ℃, with low coercivity and moderate magnetization were coated with chitosan and subjected to induction heating experiments. The coercivity of the coated nanoparticles was significantly lower compared to the uncoated nanoparticles. Among the compositions, Co_0.88Cu_0.12Fe₂O₄ exhibited superior performance, demonstrating long-term water stability and the achieved high specific absorption rate (224 W/g) and intrinsic loss power (0.89 nHm²/kg) indicating that it would be an excellent candidate as a heating agent for magnetic hyperthermia applications.

Graphical abstract