Fig. 6. Variation of the in-phase (χ′) and out-of-phase (χ′′) magnetic AC susceptibilities with the frequency of the alternating magnetic field of aqueous suspensions of a coated and uncoated ε-Fe₂O₃ NPs, and b coated and uncoated γ-Fe₂O₃ NPs. Low and high frequency ranges used in SAR experiments are shaded green and orange, respectively. The ac susceptibility is normalized to total mass of iron(iii) oxide (to give the mass susceptibility).