Exchange anisotropy modification in NiO/NiFe bilayers by ion bombardment

The dose dependence of the exchange bias field modification by He-ion bombardment in an applied magnetic field was investigated for an oxidic antiferromagnet/ferromagnet bilayer system consisting of NiO/NiFe in continuation of previous investigations for metallic antiferromagnet/ferromagnet systems (FeMn/NiFe, PtMn/NiFe, CrMn/NiFe). For low ion doses (<1.5 x 10(15) ions/cm(2)), in a magnetic field applied parallel to the as-grown exchange bias field direction, the exchange bias field H-eb is enhanced compared to the as-grown field H-eb,H-0, i.e. H-eb/H-eb,H-0 > 1. For higher doses, the relative exchange bias field H-eb/H-eb,H-0 is found to decrease gradually with increasing dose to roughly zero. Bombardment with low doses in a magnetic field applied antiparallel to the direction of H-eb,H-0 results in magnitudes of \H-eb/H-eb,H-0\ > 1 and reverses the sign of H-eb, For higher ion doses H-eb again approaches zero. These findings are similar to the findings for the bilayer system FeMn/NiFe, but differ to those for the systems PtMn/NiFe and CrMn/NiFe. The experimental results are compared with a simulation using the SRIM code. (C) 2003 Elsevier Science B.V. All rights reserved.