Tailoring Interfacial Exchange Anisotropy in Hard–Soft Core-Shell Ferrite Nanoparticles for Magnetic Hyperthermia Applications

Magnetically hard–soft core-shell ferrite nanoparticles are synthesized using an organometallic decomposition method through seed-mediated growth. Two sets of core-shell nanoparticles (S1 and S2) with different shell (Fe3O4) thicknesses and similar core (CoFe2O4) sizes are obtained by varying the initial quantities of seed nanoparticles of size 6.0 ± 1.0 nm. The nanoparticles synthesized have average sizes of 9.5 ± 1.1 (S1) and 12.2 ± 1.7 (S2) nm with corresponding shell thicknesses of 3.5 and 6.1 nm. Magnetic properties are investigated under field-cooled and zero-field-cooled conditions at several temperatures and field cooling values. Magnetic heating efficiency for magnetic hyperthermia applications is investigated by measuring the specific absorption rate (SAR) in alternating magnetic fields at several field strengths and frequencies. The exchange bias is found to have a nonmonotonic and oscillatory relationship with temperature at all fields. SAR values of both core-shell samples are found to be considerably larger than that of the single-phase bare core particles. The effective anisotropy and SAR values are found to be larger in S2 than those in S1. However, the saturation magnetization displays the opposite behavior. These results are attributed to the occurrence of spin-glass regions at the core-shell interface of different amounts in the two samples. The novel outcome is that the interfacial exchange anisotropy of core-shell nanoparticles can be tailored to produce large effective magnetic anisotropy and thus large SAR values.

Synthesis Factors Dependence of Magnetic Properties of CoFe2O4 and CoFe2-xGdxO4 Semicrystalline Nanoparticles with desired Morphology through Hydrothermal Procedure

In the present study, CoFe2O4 and CoFe2-xGdxO4 nanoparticles were synthesized by the hydrothermal process. The CoFe2O4 nanoparticles were synthesized at different temperatures (70oC, 100oC, 150oC, and 200oC), molar ratio of CoCl2/ FeCl3 (0/2, 0.75/2, 1/2, 1.5/2, and 2/2). Gadolinium-doped cobalt ferrite (CoFe2-xGdxO4) nanoparticles have also been synthesized with Gd/Fe molar ratios of 0.18 and 0.53. The XRD patterns indicate that cobalt ferrite and Gadolinium-doped cobalt ferrite nanoparticles have been successfully synthesized without impurities with a medium degree of crystallinity. The XRD patterns show that by increasing the synthesis temperature from 70oC to 200oC, the size of the nanoparticles decreased from 50.49nm to 32.45nm while the morphology of the nanoparticles also changed from a shapeless and agglomerated state to a spherical shape. The XPS curve illustrated several peaks corresponding to Fe+3, Co+2, and O 1s. The binding energies for Co and Fe were consistent with Fe 2p and Co 2p binding energies for cobalt ferrite nanoparticles. The magnetic saturation value (Ms) increased from 17.253 emu/g to 54.438 emu/g with a rise in the synthesis temperature. The effects of FeCl3/CoCl2 molar ratio on the magnetic properties showed the highest value of Ms (54.438 emu/g) and the coercivity (HC) of 744.56 Oe for a 2/1 molar ratio. The addition of gadolinium to the composition resulted in a reducing of the magnetic properties of nanoparticles; accordingly, the amount of saturated magnetization was reduced to 22.469 emu/g. Another effect of gadolinium dopant in the composition was a change in nanoparticle morphology from spherical to rod shape. The final aim of this study was to investigate the possible utilization of CoFe2O4 and CoFe2-xGdxO4 nanoparticles in medical treatment in the near future.

Combustion-assisted green-synthesized magnesium-doped cadmium ferrite nanoparticles for multifunctional applications

Magnesium-doped cadmium ferrite nanoparticles, MgXCd1−XFe2O4 (where, X = 0, 0.2, 0.4, 0.6, 0.8, 1) were synthesized by a combustion method using curd as fuel.