Highly Cyclable Voltage Control of Magnetism in Cobalt Ferrite Nanopillars for Memory and Neuromorphic Applications

Research in digital memory is growing with the increase in popularity of artificial intelligence, machine learning, Internet of Things, and Big Data. This in turn has caused an energy demand that has triggered innovation towards non-volatile memory technologies that do not require continuous power supply. Magnetic memory is a promising non-volatile technology for storing data, but conventional magnetic memory concepts use electrical current to control magnetic properties (i.e. through electromagnets or spin-torque effects) and this can lead to significant energy loss by heat dissipation. On the other hand, tuning the properties of magnetic materials by voltage-driven ion migration (magneto-ionics) gives potential for energy-efficient, non-volatile magnetic memory and neuromorphic computing.<br/><br/>Our study shows large changes in both the magnetic moment at saturation (m_S) and coercivity (H_C), of 34% and 78%, respectively, in an array CoFe₂O₄ (CFO) epitaxial nanopillar electrodes (~50 nm diameter, ~ 70 nm pitch, and 90nm in height) with applied voltage of –10 V in a liquid electrolyte cell. Furthermore, a magneto-ionic response faster than 3 s and endurance &gt;2,000 cycles are demonstrated. The response time is faster than for other magneto-ionic films of similar thickness, and cyclability is around two orders of magnitude higher than for other oxygen magneto-ionic systems. Using a range of characterisation techniques, the magnetic switching is shown to arise from modulation of oxygen content in the CFO. Also, the highly cyclable, self-assembled nanopillar structures were demonstrated to emulate various synaptic behaviours, exhibiting non-volatile, multilevel magnetic states for analog computing and high-density storage. Overall, CFO nanopillar arrays offer potential to be used as interconnected synapses for advanced neuromorphic computing applications.