Tuning of the Dzyaloshinskii-Moriya Interaction by He$^+$ ion irradiation

We studied the impact of He$^+$ irradiation on the Dzyaloshinskii-Moriya interaction (DMI) in Ta/Co20Fe60B20/Pt/MgO samples. We found that irradiation with of 40 keV He$^+$ ions increases DMI by approximately 20% for fluences up to 2$\cdot$10$\rm{^{16}}$ $\rm{ions/cm}^2$ before it decreases for higher fluence values. In contrast, the interfacial anisotropy shows a distinctly different fluence dependence. To better understand the impact of the ion irradiation on the Ta and Pt interfaces with the Co20Fe60B20 layer, we carried out Monte-Carlo simulations, which showed an expected increase of disorder at the interfaces. A moderate increase in disorder can increase the total number of triplets for the three-site exchange mechanism and can consequently increase the DMI. Our results demonstrate that the DMI can be locally engineered at the nanometer scale, providing a highly promising approach to advance skyrmion-based memories.