Effect of Ga~+ irradiation in molecular-beam epitaxy grown Pt/Co/Pt thin films studied by magneto-optic spectroscopy

摘要

In-depth profile changes induced by Ga~+ ion irradiation in Pt(5nm)/Co(3.3nm)/Pt(20nm)/ Mo(20 nm) sandwiches MBE grown on Al_2O_3 substrates are deduced from complex magneto-optic polar Kerr effect (PMOKE) measurements at photon energies between 1 and 5eV. The Ga~+ irradiation stimulates a redistribution of Pt and Co and leads to broadening of alloyed regions at Pt-Co and Co-Pt interfaces, which is evaluated using PMOKE spectra. The effect of four Ga~+ fluences D between zero and 6 × 10~(15) Ga~+/cm~2 was studied. The observed PMOKE azimuth rotation peak centered at 4.5 eV reaches the maximum of 0.42° at D = 1 × 10~(15) Ga~+/cm~2 and becomes thus enhanced by a factor of 3.2 with respect to that in the non-irradiated sample. At D = 6× 10~(15) Ga~+/cm~2 the peak amplitude falls to 0.05°. To find the in-depth profile of Co concentration s in the sandwiches as a function of D, the PMOKE azimuth rotation and ellipticity spectra are compared with a multilayer model, where ideal flat interfaces are replaced by sequences of Co_sPt_(1-s) layers. The dependence on D is compared with that evaluated by simulations of the structural effects of ion irradiation. At the highest D, the irradiation produces an almost complete erosion of the top Pt and Co accompanied by mixing at the Pt-Mo interface.