HIGH-ENERGY IRRADIATION OF MAGNETIC INSULATORS BY LEAD IONS - APPEARANCE OF A PLATEAU IN THE DAMAGE EFFICIENCY

Lead irradiation with an incident energy of 5.6 GeV has been used to study the induced damage in magnetic insulators (Y3Fe5O12, BaFe12O19, NiFe2O4) for high values of the electronic stopping power (dE/dx). Using Mossbauer spectrometry, the damage efficiency epsilon = A/(dE/dx), where A is the damage cross section, is extracted and compared to previous results. Saturation of the damage efficiency is confirmed, and in the range of dE/dx studied in our experiments the damage yield is proportional to the deposited energy. The damage efficiency in Y3Fe5O12 and BaFe12O19 is fitted by a saturation law using the relation epsilon = epsilon-max(1-exp(-k(dE/dx)n)). A unique value of n = 4 is extracted while epsilon-max and k depend on the irradiated materials. Epsilon-max leads to a value indicating that the maximum damage efficiency arises when 5 eV is deposited on each atom. Using n = 4, this saturation law was applied with success to the spinel NiFe2O4 and to the amorphous alloy a-Fe85B15.