Enhanced visible-light manipulation of the ferromagnetism in 3D cobalt nanosphere by sphere size engineering

Rapid and energy-efficient magnetization control is essential for advancing next-generation magnetic sensors and memory technologies. Photovoltaic gating of magnetism via light irradiation leverages advances in solar-cell engineering and electric-field-controlled magnetism, offering enhanced tunability at reduced power consumption. In this study, we report the fabrication of a cobalt nanosphere-photovoltaic material thin-film device. By systematically tuning the nanosphere diameter, concentration, and film thickness, we achieved an 11.5% reduction in magnetization under visible-light illumination (200 mW/cm2, 6.93 × 1017 photons cm−2 s−1). Notably, the relative magnetization reduction scales linearly with 1/r2, where r is the effective nanosphere radius. This behavior is attributed to a surface-electrical potential conservation mechanism, suggesting that increasing the surface-area-to-volume ratio enhances magneto-optical tunability. These insights provide a rational design strategy for light-modulated magnetic nanodevices with potential applications in reconfigurable sensors and memory elements.