Magnetic fluid hyperthermia has been recently considered as a Renaissance of cancer treatment modality due to its remarkably low side effects and high treatment efficacy compared to conventional chemotheraphy or radiotheraphy. However, insufficient AC induction heating power at a biological safe range of AC magnetic field (H_appl ·f_appl < 3.0-5.0 × 10⁹ A m^-1 s^-1 ), and highly required biocompatibility of superparamagnetic nanoparticle (SPNP) hyperthermia agents are still remained as critical challenges for successful clinical hyperthermia applications. Here, newly developed highly biocompatible magnesium shallow doped γ-Fe₂ O₃ (Mg_0.13 -γFe₂ O₃ ) SPNPs with exceptionally high intrinsic loss power (ILP) in a range of 14 nH m² kg^-1 , which is an ≈100 times higher than that of commercial Fe₃ O₄ (Feridex, ILP = 0.15 nH m² kg^-1 ) at H_appl ·f_appl = 1.23 × 10⁹ A m^-1 s^-1 are reported. The significantly enhanced heat induction characteristics of Mg_0.13 -γFe₂ O₃ are primarily due to the dramatically enhanced out-of-phase magnetic susceptibility and magnetically tailored AC/DC magnetic softness resulted from the systematically controlled Mg²⁺ cations distribution and concentrations in octahedral site Fe vacancies of γ-Fe₂ O₃ instead of well-known Fe₃ O₄ SPNPs. In vitro and in vivo magnetic hyperthermia studies using Mg_0.13 -γFe₂ O₃ nanofluids are conducted to estimate bioavailability and biofeasibility. Mg_0.13 -γFe₂ O₃ nanofluids show promising hyperthermia effects to completely kill the tumors.

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