Mossbauer spectra (MS) and differential scanning calorimetry (DSC) were used to study the effect of natural ageing during a period of seven years on the magnetic properties, thermal stability and the resistivity to y-irradiation of the ferromagnetic metallic glass systems Fe78B13Si9 and Fe77Cr2B16Si5. Small ordering and rearrangement of the constituent atoms caused an increase in average value of the hyperfine field distribution as well as a decrease in the distribution width were observed due to the effect of natural ageing. The ageing also affected the direction of the net magnetic moments. A decrease in the resistance to y-irradiation in addition to a decrease in thermal stability upon ageing were found to be dependent on the composition of the investigated samples.
