Abstract
We investigated a new type of multilayer film for Nanomagnetic Logic with perpendicular anisotropy (pNML) enhanced by the Dzyaloshinskii-Moriya interaction (DMI). The DMI effect provides an additional energy term and widens the design space for pNML film optimization. In this work we added an Ir layer between Co and Pt to our standard pNML multilayer (ML) film stack - [Co/Pt]x4. Multilayer stacks of films with and w/o Ir were sputtered and patterned to nanowires of 400 nm width by means of focused ion beam lithography (FIB). For comparability of the films they were tuned to show identical anisotropy for multilayer stacks with and w/o Ir. The field-driven domain wall (DW) velocity in the nanowires was measured by using wide-field MOKE microscopy. We found a strong impact of Ir on the DW velocity being up to 2 times higher compared to the standard [Co/Pt]x4 ML films. Moreover, the maximum velocity is reached at much lower magnetic field, which is beneficial for pNML operation. These results pave the way for pNML with higher clocking rates and at the same time allow a further reduce power consumption.
Highlights
Nanomagnetic Logic (NML) is one of the most mature and favorable candidates for the Beyond CMOS scaling era and is listed in the latest International Technology Roadmap for Semiconductors 2015 (ITRS) in the “Beyond CMOS” technology Chapter.[1]
In Ir enhanced ML films the maximum velocity of 78m/s is reached at much lower field (120mT), while in multilayer films without Ir vDW starts to saturate at around 150mT and reaches only 42m/s
This could be due to the lack of precise control of Ga + ions dose during focused ion beam lithography (FIB) irradiation of the artificial nucleation center (ANC)
Summary
Nanomagnetic Logic (NML) is one of the most mature and favorable candidates for the Beyond CMOS scaling era and is listed in the latest International Technology Roadmap for Semiconductors 2015 (ITRS) in the “Beyond CMOS” technology Chapter.[1]. Depending on the clocking field strength and multilayer film parameters (mainly damping constant) nucleation is reported to take less than fraction of a nanosecond.[12] In comparison, maximum domain wall speed in common pNML Co/Pt multilayer films saturates at around 40m/s, the time needed to propagate the new nucleated domain through the whole magnet takes several tens of nanoseconds To address this issue we enhanced the standard [Co/Pt]x4 pNML film stack by adding the Ir layer on top of each layer of Co. As reported in recent research, braking the symmetry of Co interfaces by inserting a heavy metal with large spin orbit coupling results in strong antisymmetric exchange interaction called Dzyaloshinskii-Moriya interaction, which is supposed significantly support the domain wall motion.[13,14]
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