Low temperature permeability and current noise of ferromagnetic pickup coils

► We evaluated the relative permeability of ferromagnetic materials at 4.2 K. ► The current noise of different ferromagnetic materials at 4.2 K was measured. ► The current noise was also calculated using the Fluctuation-Dissipation-Theorem. ► Calculation and measurement of the current noise showed a good coincidence. ► We found promising core materials for a Cryogenic Current Comparator.