Modifications of magnetic properties of Pt/Co/Pt thin layers by focused gallium ion beam irradiation

We show how the magnetic properties of the Pt/Co ultrathin film structure can be modified and even controlled under uniform irradiation by Ga+ ions at low fluence in the 20-100 keV range. A systematic magneto-optical study is presented for the Pt/Co(1.4 nm)/Pt(111) ultrathin-film structure. At ion fluences below D=10(14) Ga+/cm(2), the coercive field is steadily reduced when increasing the fluence. At large fluences, in the range D=(5-10)x10(14) Ga+ ions/cm(2), the magnetization of the Co layer drops rapidly and the film finally becomes paramagnetic at room temperature for D>2x10(15) Ga+ ions/cm(2). We demonstrate that these magnetic changes are related to the effect of ion-induced collisional intermixing of the Co/Pt interfaces, leading to the formation of stable Co-Pt alloys with varying composition across the interfaces. A simple model is derived to relate the ion beam-induced mixing to the changes in magnetic properties. The present work allows us to gain a quantitative understanding of previous experiments using a focused Ga+ ion beam to pattern magnetic properties of similar samples at a sub-100 nm scale. (C) 2002 American Institute of Physics.