Magnetic torque of the ferromembrane, in units of the thermal energy, as a function of the magnetic susceptibility κ and thickness of the magnetic layer between the inner and outer ellipsoid t (2c = 35 µm, for theoretical modelling, 2a = 2b = 7 µm, local geomagnetic field strength 0.3 Oe). λ is the ratio of similitude between outer and inner ellipsoid.