  Taking advantage of the anomalous Hall effect, we electrically probe
low-frequency magnetization fluctuations at room temperature in a thin
ferromagnetic Pt/Co/AlO$_x$ layer stack with perpendicular magnetic anisotropy.
We observe a strong enhancement of the Hall voltage fluctuations within the
hysteretic region of the magnetization loop. Analyzing both the temporal
evolution of the anomalous Hall voltage and its frequency-dependent noise power
density, we identify two types of magnetic noise: abrupt changes in the
magnetic domain configuration, evident as Barkhausen-like steps in the Hall
voltage time trace, yield a noise power density spectrum scaling with frequency
as $1/f^{\beta}$ with $\beta\approx 1.9$. In contrast, quasi-stationary
magnetization configurations are connected with a magnetic noise power density
with an exponent $\beta\approx 0.9$. The observation of Barkausen steps and
relaxation effects shows that the magnetic system is in a non-stationary state
in the hysteresis region, such that the fluctuation-dissipation theorem cannot
be expected to hold. However, the time-dependent change in the Hall voltage for
constant magnetic field strength resembles the integrated noise power.
