X-ray absorption analysis of sputter-grown Co/Pt stackings before and after helium irradiation

We have studied the local order around cobalt atoms in Pt/Co/Pt layered sys tems gradually modified by irradiation using 30 keV helium ions. Using X-ra y diffraction and X-ray Absorption Fine Structure, we have determined the c rystallographic order, the number of Co-Co and Co-Pt bonds and the correspo nding bond lengths both in-plane and in the perpendicular direction. The co mparison with an interdiffusion model highlights the unexpected complexity of the initial Pt/Co/Pt nanostructure. We use the Neel/Bruno model of magne tic anisotropy to correlate the structure and the magnetic hysteresis prope rties. We then identify the structural consequences of irradiation onto the short range order. The irradiation induces a substitutional mixing maintai ning the initial crystallographic structure. We confirm that the mixing rat e is in agreement with a ballistic mechanism of mixing. In addition, we sho w that the previously reported irradiation-induced controlled decrease of t he magnetic anisotropy can not be solely attributed to Co-Pt intermixing: i rradiation also significantly releases the 3.4% tensile strain of the cobal t-rich dense planes. We finally speculate on the class of magnetic material s the concept of light ion irradiation could be extended to.