Voltage control of magnetism in Ni-Co oxide mesoporous films : impact of porosity on oxygen magneto-ionics performance

Control of magnetism through electric-field-driven migration of ions, referred to as magneto-ionics (MI), holds promise for the development of non-volatile energy-efficient memory storage, as well as spintronic, neuromorphic and magnetoelectric devices. Here, we study the MI phenomena in 350 nm thick Ni55Co45 oxide films with varying degrees of porosity, obtained by electrodeposition of the parent Ni-Co metallic alloy on metallized Si substrate and subsequent annealing in air. Annealing at 450 degrees C of the film electrodeposited from a P-123-containing electrolyte with Ni and Co sulfate salts yields a Ni-Co oxide that partially retains its mesoporosity. This sample exhibits a higher MI response compared to a low-porosity (nearly dense) Ni-Co oxide film, indicating that an increased surface-to-volume ratio enhances MI. Comprehensive characterization of the mesoporous Ni-Co oxide-coated Si/Ti/Au sample reveals that annealing not only oxidizes the top approximate to 100 nm of the Ni-Co film but also induces silicon diffusion. MI phenomena occur via O2- migration out of and into the top Ni-Co oxide layer under negative and positive biasing, respectively. While the system shows some irreversibility, endurance improves significantly as cycling frequency increases, evidencing the potential of this material for voltage-tunable memory applications.