Interface engineering by He+ ion irradiation

One elegant approach to engineer magnetic materials  is the use of light He ion irradiation that has been demonstrated to be extremely efficient in controlling at the atomic scale the magnetic properties of magnetic thin films and multilayers, since only interatomic displacements are induced with no cascade collisions. In collaboration with the spin-off company Spin-Ion Technologies launched in 2017, we have extensively investigated the effect of He ion irradiation on the structural and magnetic properties of CoFeB-MgO ultra-thin films with perpendicular anisotropy. Several important results based on the precise control of interface intermixing have been demonstrated: enhancement of the Dzyaloshinskii-Moriya interaction, increase of domain wall velocity, enhancement of all optical switching, creation and chanelling of skyrmions, control of skyrmion density, multi-level swithing in Spin Orbit Torque devices, control of metal insulator transition, reduction of linewidth in nano-oscillators….

Fig. 1: Focused He+ ion irradiation can be used to create and guide skyrmions in racetracks

Spin-orbit torque driven multilevel switching in He+ irradiated W-CoFeB-MgO Hall bars

We have investigated the spin–orbit torque-driven magnetization switching in W/CoFeB/MgO Hall bars with perpendicular magnetic anisotropy. He+ ion irradiation through a mask has been used to reduce locally the effective perpendicular anisotropy at a Hall cross. Anomalous Hall effect measurements combined with Kerr microscopy indicate that the switching process is dominated by domain wall (DW) nucleation in the irradiated region followed by rapid domain propagation at a current density as low as 0.8 MA/cm2 with an assisting in-plane magnetic field. Thanks to the implemented strong pinning of the DW at the transition between the irradiated and the non-irradiated region, an intermediate Hall resistance state is induced, which is further verified by finite element simulations. Such a method to control electrically multi-level resistances using He+ ion irradiation shows great potential in realizing neuromorphic and memristor-like magnetic devices.

Fig. 2: Local He+ ion irradiation enables the deterministic Spin-Orbit Torque driven switching of Hall cross

Collaborations: Spin-Ion Technologies, Laboratoire de Physique des solides, Laboratoire Albert Fert and Spintec in France. CNR et INRIM in Italy, Singulus Technologies and Mainz University in Germany, New York university USA, Salamanca University in Spain, Georgetown university, USA