Directional effects of heavy-ion irradiation in Tb/Fe multilayers

Deposition of a ${}^{57}\mathrm{Fe}$ probe layer at the top of iron layers in Tb/Fe multilayers has allowed us to study locally the atomic mixing induced by high-energy heavy-ion irradiation at the Tb-on-Fe interface. The structural and magnetic transformations induced by ion irradiation of the probe layer were investigated by ${}^{57}\mathrm{Fe}$ conversion electron M\"ossbauer spectrometry. To study directional effects of the ion beam, we have irradiated a stack of two pieces of the same multilayer set face to face. No change in the average composition of the mixed Tb-on-Fe interface was observed when the incident ion direction is changed from a Tb layer to a Fe layer, or from a Fe layer to a Tb layer.