  We demonstrate the tracking of the spin dynamics of ensemble and individual
magnetic ferritin proteins from cryogenic up to room temperature using the
nitrogen-vacancy color center in diamond as magnetic sensor. We employ
different detection protocols to probe the influence of the ferritin
nanomagnets on the longitudinal and transverse relaxation of the
nitrogen-vacancy center, which enables magnetic sensing over a wide frequency
range from Hz to GHz. The temperature dependence of the observed spectral
features can be well understood by the thermally induced magnetization
reversals of the ferritin and enables the determination of the anisotropy
barrier of single ferritin molecules.
