Study on the chemical co-precipitation synthesized CoFe2O4 nanoparticle for magnetocaloric performance in the vicinity of superparamagnetic blocking temperature.

Nanoscaled magnetic cobalt ferrite (CoFe2O4) of approximately size 17 nm was synthesized via the co-precipitation method and then annealed at 600 °C. The resultant materials were taken for various magnetic characterizations. The X-ray diffraction pattern confirms the formation of the fcc type of cubic crystal structure. The ferrimagnetic phenomenon of the specimen was confirmed by the hysteresis loop, which is comparable to the slow relaxation sextet pattern of the MÓ§ssbauer study. Isomer shift, quadrupole splitting, hyperfine field, and Fe3+ occupancy of various sites are also investigated from mÓ§ssbauer spectroscopy. The frequency-dependent initial permeability has a comparatively high value up to a certain frequency range and then decreases drastically, whereas the imaginary part of complex permeability decreases sharply with the increase of frequency. The temperature-dependent magnetization ensures the presence of a superparamagnetic blocking temperature of 433 K. In the study of the magnetocaloric effect, isothermal magnetization measurements were carried out around the superparamagnetic blocking temperature, revealing a maximum entropy change of ΔSmax = 1.32 J/kg K and a relative cooling power (RCP) of 52.22 J/kg (H = 1.5 T) through the Maxwell approach. These outcomes emphasize the potential of CoFe2O4 NPs for magnetic refrigeration at reduced temperatures with lower applied magnetic fields.

Thermo-therapeutic applications of chitosan- and PEG-coated NiFe2O4 nanoparticles.

The paper reports the thermo-therapeutic applications of chitosan- and PEG-coated nickel ferrite (NiFe2O4) nanoparticles. In this study NiFe2O4 nanoparticles were synthesized by the co-precipitation method, tuning the particle size through heat treatment in the temperature range from 200-800 °C for 3 h. XRD and TEM analysis revealed that the the ultrafine nanoparticles were of size 2-58 nm. Crystallinity of the NiFe2O4 nanoparticles in the as-dried condition with the particle size ∼2-3 nm was confirmed from the presence of a lattice fringe in the HRTEM image. VSM measurements showed that a superparamagnetic/ferromagnetic transition occurs with increasing particle size, which was further confirmed by Mössbauer spectroscopy. The nickel ferrite nanoparticles with optimum particle size of 10 nm were then coated with materials commonly used for biomedical applications, i.e. chitosan and PEG, to form homogeneous suspensions. The hydrodynamic diameter and the polydispersity index (PDI) were analyzed by dynamic light scattering at the physiological temperature of 37 °C and found to be 187 nm and 0.21 for chitosan-coated nanoparticles and 285 nm and 0.32 for PEG-coated ones. The specific loss power of rf induction heating by the set-up for hyperthermia and r 2 relaxivity by the nuclear magnetic resonance were determined. The results of induction heating measurements showed that the temperature attained by the nanoparticles of size 10 nm and concentration of about 20 mg ml(-1) was >70 °C (for chitosan) and >64 °C (for PEG). It has been demonstrated that the required temperature for hyperthermia heating could be tuned by tuning the particle size, shape and magnetization and the concentration of solution. For other potential biomedical applications of the NiFe2O4 nanoparticle solution, e.g. magnetic resonance imaging, the NMR studies yielded the T 1 and T 2 relaxivities as 0.348 and 89 mM(-1) s(-1) respectively. The fact that the T 2 relaxivity is orders of magnitude higher than T 1 indicates that this is suitable as a T 2 contrast agent for magnetic resonance imaging.