  Muon Spin Rotation is employed to investigate the spin dynamics of ferritin
proteins isolated from the brain of an Alzheimer's disease (AD) patient and of
a healthy control, using a sample of horse-spleen ferritin as a reference. A
model based on the N\'eel theory of superparamagnetism is developed in order to
interpret the spin relaxation rate of the muons stopped by the core of the
protein. Using this model, our preliminary observations show that ferritins
from the healthy control are filled with a mineral compatible with
ferrihydrite, while ferritins from the AD patient contain a crystalline phase
with a larger magnetocrystalline anisotropy, possibly compatible with magnetite
or maghemite.
