MeV Si+ irradiation of Fe/Ni bilayers: influence of microstructural and interfacial changes on magnetic properties

The effects of microstructural changes during low-temperature MeV Si+ ion-b eam irradiation on the magnetic properties of Fe (500 Angstrom)/Ni (500 Ang strom) bilayers deposited onto thermally oxidized Si have been studied as a function of ion dose. The as-deposited films exhibit strong Ni(111)/Fe(011 ) texture with sharp interfaces. Upon irradiation, grains grow progressivel y within each layer but this process stops abruptly at the Ni-Fe interface. The resistivity and the anisotropic magnetoresistance are virtually unchan ged by irradiation up to 10(16) ions cm(-2). Higher doses, however, lead to an in-plane unidirectional anisotropy as well as asymmetric magnetoresista nce and magnetization curves which arise from interactions between the ferr omagnetic layers and the magnetic oxide lavers formed at the top surface an d the substrate interface during ion irradiation. (C) 2001 Elsevier Science B.V. All rights reserved.