To investigate the role of magnetic anisotropy on magnetic hyperthermia heating efficiency at low field conditions, Mn, MnZn, and MnCo-ferrite nanoparticles were synthesized using the hydrothermal method. The coercive field temperature dependence method was used to determine the blocking temperature distribution of the particles by considering the temperature dependence of anisotropy and magnetization and the random anisotropy axis configuration. The data allowed one to estimate the room-temperature quasi-static superparamagnetic diameter, which was found to be lower than the theoretical value. Magnetic hyperthermia experiments of the magnetic nanocolloids at 522 kHz indicated that soft nanomagnets heat more efficiently at clinically relevant conditions. The heating performance was found to decrease at the higher fraction of blocked nanoparticles. For instance, samples with similar size distribution and mean diameter of 10 nm, at a field amplitude of only 120 Oe (9.6 kA m–1), showed a decrease of specific loss power of 56% for the Mn-ferrite and 93% for the MnCo-ferrite in comparison with the MnZn-ferrite nanoparticle. The fractions of blocked particles of the MnZn, Mn, and MnCo-ferrite were 5, 10, and 25%, respectively, at room temperature.

Multifunctional magnetic nanoparticles (NPs) that can generate and monitor heat (in real-time) during thermal therapy are a major challenge in nanomedicine. Here, we report a trimodal system combining magnetic NP hyperthermia (MNH), photothermal therapy (PTT), and luminescent nanothermometry (LNT) properties with an all-in-one nanoplatform. Zinc–manganese ferrite NPs were optimized focusing on low field MNH, where Zn0.3Mn0.7Fe2O4 proved as a competitive nanoheater at clinically relevant conditions. Further, SiO2-coated Zn0.3Mn0.7Fe2O4/cit. with embedded Nd3+ (Zn0.3Mn0.7Fe2O4@SiO2:Nd) NPs were prepared for the potency of multifunctionality as LNT and enhanced PTT. Photothermal conversion efficiency (PCE), at low laser power conditions (1.5 W/cm2), varied from 17% for silica-coated magnetic NPs to 24% after embedding 1 mmol of Nd3+ in the SiO2 matrix. Increasing laser power to 11.8 W/cm2 decreased the PCE of Zn0.3Mn0.7Fe2O4@SiO2:Nd to 9%, but this deleterious effect was reduced significantly by the shell engineering strategy, that is, increasing the shell thickness Zn0.3Mn0.7Fe2O4@ SiO2@SiO2:Nd that maintained a PCE value of 18%. Additionally, as a potential nanothermometer, with excitation around 800 nm and emission at the second biological window, the thermal sensitivity of the system was found to be ∼1.1 % K–1 at 300 K (27 °C), ∼ 1.4% K–1 at 316 K (43 °C), and ∼1.5% K–1 at 319 K (46 °C). Additionally, simultaneous heating effects due to magnetic fields and photoexcitation (808 nm) on Zn0.3Mn0.7Fe2O4@SiO2@SiO2:Nd show synergy effects between MNH and PTT. Because of the high hemolytic activity toward the red blood cells due to the SiO2 layer, we also demonstrate that surface coating the nanocarrier with bovine serum albumin drastically reduced the hemolytic activity providing a capability for future in vivo applications with this multifunctional nanocarrier.

Recently, the development of an alternative magnetic refrigerant for the conventional fossil fuels attracts the researchers. We discussed the structural defect-induced magnetocaloric effect (MCE) in Ni0.3Zn0.7Fe2O4/graphene (NZF/G) nanocomposites for the first time. Single-phase spinel ferrite nanocomposites with an average size of 7–11.4 nm were achieved by using the microwave-assisted coprecipitation method. The effect of graphene loading on the structural and magnetism of NZF/G nanocomposites was elaborated. Raman analysis proved that the interface interaction between NZF and graphene yielded different densities of structural defects. In view of magnetism, superparamagnetic NZF nanoparticles showed a magnetic entropy change (−ΔS M max) of −0.678 J·kg–1 K–1 at 135 K, whereas the NZF/G nanocomposites exhibited superior −ΔS M max at cryogenic temperatures and the defect-induced MCE change was indeed similar to the I D/I G intensity ratio. The nanocomposites exhibited different magnetic orderings between 5 and 295 K, and it was varying for I D/I G, 1.83 > 1.68 > 1.57 as antiferromagnetic (AFM) > AFM/ferrimagnetic (FiM) > FiM, respectively. Till now, NZF/G nanocomposites showed an inverse MCE of 4.378 J·kg–1 K–1 at 35 K and a refrigerant capacity of 88 J·kg–1 for 40 kOe, which was greater than the ferrites reported so far. Finally, MCE and magnetic hyperthermia were correlated at ambient conditions. These results pave the way for ferrite/graphene nanocomposites for cooling applications.

Controlling populations of free-roaming dogs and cats poses a huge challenge worldwide. Non-surgical neutering strategies for male animals have been long pursued, but the implementation of the procedures developed has remained limited to date. As submitting the testes to high temperatures impairs spermatogenesis, the present study investigated localized application of magnetic nanoparticle hyperthermia (MNH) to the testicles as a potential non-surgical sterilization method for animals. An intratesticular injection of a magnetic fluid composed of manganese-ferrite nanoparticles functionalized with citrate was administered followed by testicle exposure to an alternate magnetic field to generate localized heat. Testicular MNH was highly effective, causing progressive seminiferous tubule degeneration followed by substitution of the parenchyma with stromal tissue and gonadal atrophy, suggesting an irreversible process with few side effects to general animal health.

The study demonstrates the performance of heating efficiency in single-phase and binary phase spinel ferrite nanosystems. Ferrimagnetic cobalt ferrite (CoFe 2 O 4) (CFO) and superparamagnetic copper ferrite/copper oxide (CuFe 2 O 4 /CuO) (CuF) nanosystems of different particle sizes were synthesized through a microwave-assisted coprecipitation method. The heating behavior was observed in range of both field amplitudes (8-24 kA/m at 516 kHz) and frequencies (325-973 kHz at 12 kA/m). The heating efficiency was analyzed and compared by means of particle size, magnetization, effective anisotropy constant, and Néel relaxation mechanism. Indeed, the heating rate was maximized in larger ferrite particles with low effective anisotropy constant. Moreover, though the magnetization and effective anisotropy constant of single-phase CoFe 2 O 4 nanoparticles were higher, the binary phase CuFe 2 O 4 /CuO nanosystems of similar crystallite size (28 nm) exhibited superior heating efficiency (4.21°C/s). For a field amplitude and frequency of 24 kA/m and 516 kHz, the heating rate of CuF and CFO ferrites with different crystallite sizes decreased in the order of 4.21 > 2.14 > 0.58 > 0.52°C/s for 29 nm > 25 nm > 12 nm > 15 nm, respectively. The results emphasize that binary phase ferrite nanoparticles are better thermoseeds than the single-phase ferrites for the magnetic hyperthermia application.