In this study, the ac magnetic hyperthermia responses of spinel CoFe 2 O 4 , MnFe 2 O 4 , and NiFe 2 O 4 nanoparticles of comparable sizes (∼20 nm) were investigated to evaluate their feasibility of use in magnetic hyperthermia. The heating ability of EDT-coated nanoparticles which were dispersed in two different carrier media, deionized water and ethylene glycol, at concentrations of 1 and 2 mg/mL, was evaluated by estimating the specific loss power (SLP) (which is a measure of magnetic energy transformed into heat) under magnetic fields of 15, 25, and 50 kA/m at a constant frequency of 195 kHz. The maximum value of SLP has been found to be ∼315 W/g for CoFe 2 O 4 and ∼295 W/g for MnFe 2 O 4 and NiFe 2 O 4 nanoparticles. We report very promising heating temperature rising characteristics of CoFe 2 O 4 , MnFe 2 O 4 , and NiFe 2 O 4 nanoparticles under different applied magnetic fields that indicate the effectiveness of these nanoparticles as hyperthermia agents.

The microstructure, composition and magnetism of CoFe 2 O 4 , MnFe 2 O 4 and NiFe 2 O 4 nanoparticles of comparable sizes (∼20 nm) and interparticle spacings (∼20 nm) have been characterized from 10 to 400 K. The cation distributions of the tetrahedral and octahedral sites of the particles, that have cubic spinel structures, have a high degree of inversion, ∼0.98 for CoFe 2 O 4 , ∼0.80 for MnFe 2 O 4 and NiFe 2 O 4 nanoparticles. The blocking temperatures were ∼300 K for the MnFe 2 O 4 and NiFe 2 O 4 nanoparticles, while the CoFe 2 O 4 nanoparticles, due to their higher intrinsic anisotropy had a significantly higher blocking temperature above 400 K. Specifically, the magnetocrystalline anisotropy of the CoFe 2 O 4 nanoparticles was K = (2.96 ± 0.03) × 10 6 ergs cm −3 , while for the MnFe 2 O 4 nanoparticles, K = (0.04 ± 0.01) × 10 6 ergs cm −3 , and for the NiFe 2 O 4 nanoparticles, K = (0.07 ± 0.01) × 10 6 ergs cm −3 . The magnetism of these three ferrite systems are discussed in detail with regards to their microstructures and cation distributions.

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