The heat dissipation from the bulk powders was measured with a fiber optic probe. Approximately 25 mg of each SPION powder was transferred to a 2 mL glass vial and placed inside a coil with nine windings. The nominal oscillation frequency was set to 588.5 kHz and the magnetic field strength to 14 mT. The heating efficiency was calculated as the rise in temperature in the initial 10 seconds.