Initial slope of the temperature variation with time, ΔT/δt, SAR deduced using the formula SAR = (ΔT/δt)⋅(Cv/XFe), where Cv = 4.2 J/gK is the specific heat capacity of water and XFe is the magnetosome concentration, and temperature increase measured over the whole magnetic session, ΔT. ΔT/δt, SAR and ΔT were measured for magnetosomes suspended in water (2 mg of magnetosomes in 100 µl of water or 40 µg of magnetosomes in 2 µl of water), magnetosomes after cellular internalization in vitro, and magnetosomes administered to U87-Luc intracranial tumors and exposed to one MS (MS1), two MS (MS2), three MS (MS3), four MS (MS4), five MS (MS5), six to fifteen MS (MS6 to MS15)