Abstract and subjects
The magnetization of native horse spleen ferritin protein is measured in pulsed magnetic fields to 55
T at
T=1.52
K. The magnetization rises smoothly with negative curvature due to uncompensated Fe
3+ spins and with a large high field slope due to the underlying antiferromagnetic ferritin core. Even at highest fields the magnetic moment is only ∼4% of the saturation moment of the full complement of Fe
3+ in the ferritin molecule. The AC magnetic susceptibility,
χ
AC(
T,
f), responding to the uncompensated spins, reaches a maximum near the superparamagnetic blocking temperature with the temperature of the maximum,
T
M, varying with excitation frequency,
T
M
−1
α
log
f for 10⩽
f⩽10
4
Hz.