Reliable control of magnetism using voltage-driven ionic transport in nitrides

What is it about?

The control of magnetic properties using voltage-driven ion motion, i.e., magneto-ionics, holds the promise to boost energy efficiency in information technologies such as spintronic devices or future non-von Neumann computing architectures. For this purpose, stability, reversibility, endurance, and ion motion rates need to be synergistically optimized. Among various ions, nitrogen has demonstrated superior magneto-ionic performance compared to classical species such as oxygen or lithium. Here, we show that ternary CoFeN compound exhibits an unprecedented nitrogen magneto-ionic response. Partial substitution of Co by Fe in binary CoN is shown to be favorable in terms of generated magnetization, cyclability and ion motion rates. Specifically, the optimized nitride exhibits significant improvements in terms of induced saturation magnetization, magneto-ionic rate, as well as endurance (over 1,000 cycles), bringing new perspectives for improved magneto-ionics by enhancing voltage-controlled ion transportation.

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Photo by Markus Spiske on Unsplash

Photo by Markus Spiske on Unsplash

Why is it important?

Voltage control of magnetism holds the potential to boost energy efficiency in low-power spintronic systems since energy dissipation by Joule heating effect might be strongly minimized compared to spin-transfer-torque devices. Within this approach, magneto-ionics stands out from other converse magnetoelectric mechanisms due to its large and non-volatile modulation of magnetism with electric fields. It was demonstrated that nitrogen magneto-ionics is favorable to oxygen magneto-ionics as regards to ion motion rates and cyclability. Our report marks further exploitation of multi-element transition-metal nitride engineering approach to push nitrogen magneto-ionics to the next level. We propose suitable structural and compositional design in magneto-ionic CoFeN nitrides as a means to drastically boost magneto-ionic effects in terms of induced saturation magnetization, reversibility and cyclability. For the first time, detailed synthesis, structural and magneto-ionic properties of ternary CoFeN are reported and compared with earlier study. Particularly, voltage-treated nitride films exhibit the highest induced saturation magnetization (1500 emu cm–3) and magneto-ionic rate (35.5 emu cm–3 s–1) reported so far for nitrogen magneto-ionics, representing 300% and 600% improvements, respectively, over the best results previously obtained in binary nitrides. Remarkably, compared to other oxides or nitrides, whose endurances are typically limited to a few tens of cycles, the endurance reported here is substantially enhanced (with cyclability above 1,000 cycles), bearing comparison with that of H+ based magneto-ionic systems but with a non-volatile feature. The work offers guidance and prospects towards improving magneto-ionics performance, and is highly relevant for the further exploitation of nitrogen magneto-ionics in forthcoming technological applications.

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