Magnetic phase diagrams of He ion-irradiated Pt/Co/Pt ultrathin films

Through the magneto-optical Kerr effect, we determined the magnetic phase diagrams of Pt/Co(t)/Pt ultrathin film structures uniformly irradiated by He ions in the (T, F) and (t, F) planes, where F is the ion fluence, T the temperature and t the Co film thickness. Three ferromagnetic states with out-of-plane, in-plane and oblique spin configurations were identified. For a fixed Co thickness, an out-of-plane state is favoured at low fluence, while in-plane and oblique states are stabilized at higher fluence. Thus, He ion irradation controls the magnetic system's gradual evolution from Ising-type to XY-type. We show that a similar evolution also occurs at room temperature when increasing the Co thickness for a given fluence value.