Magnetic Ni‐Nanoinclusions in VO₂ Thin Films for Broad Tuning of Phase Transition Properties

Abstract Mott insulator VO 2 exhibits an ultrafast and reversible semiconductor‐to‐metal transition (SMT) near 340 K (67 °C). In order to fulfill the multifunctional device applications, effective transition temperature ( T c ) tuning as well as integrated functionality in VO 2 is desired. In this study, multifunctionalities including tailorable SMT characteristics, ferromagnetic (FM) integration, and magneto‐optical (MO) coupling, have been demonstrated via metal/VO 2 nanocomposite designs with controlled morphology, i.e., a two‐phase Ni/VO 2 pillar‐in‐matrix geometry and a three‐phase Au/Ni/VO 2 particle‐in‐matrix geometry. Evident T c reduction of 20.4 to 54.9 K has been achieved by morphology engineering. Interestingly, the Au/Ni/VO 2 film achieves a record‐low T c of 295.2 K (22.2 °C), slightly below room temperature (25 °C). The change in film morphology is also correlated with unique property tuning. Highly anisotropic magnetic and optical properties have been demonstrated in Ni/VO 2 film, whereas Au/Ni/VO 2 film exhibits isotropic properties because of the uniform distribution of Au/Ni nanoparticles. Furthermore, a strong MO coupling with enhanced magnetic coercivity and anisotropy is demonstrated for both films, indicating great potential for optically active property tuning. This demonstration opens exciting opportunities for the VO 2 ‐based device implementation towards smart windows, next‐generation optical‐coupled switches, and spintronic devices.