  We report maximized specific loss power and intrinsic loss power approaching
theoretical limits for AC magnetic field heating of nanoparticles. This is
achieved by engineering the effective magnetic anisotropy barrier of
nanoparticles via alloying of hard and soft ferrites. 22 nm
Co0.03Mn0.28Fe2.7O4/SiO2 NPs reached a specific loss power value of 3417
W/gmetal at a field of 33 kA/m and 380 kHz. Biocompatible Zn0.3Fe2.7O4/SiO2
nanoparticles achieved specific loss power of 500 W/gmetal and intrinsic loss
power of 26.8 nHm2/kg at field parameters of 7 kA/m and 380 kHz, below the
clinical safety limit. Magnetic bone cement achieved heating adequate for bone
tumor hyperthermia, incorporating ultralow dosage of just 1 wt% of
nanoparticles. In cellular hyperthermia experiments, these nanoparticles
demonstrated high cell death rate at low field parameters. Zn0.3Fe2.7O4/SiO2
nanoparticles show cell viabilities above 97% at concentrations up to 0.5 mg/ml
within 48 hrs, suggesting toxicity lower than that of magnetite.
