Novel single-crystalline Hf1−xTixO2 1D nanostructures with room-temperature ferromagnetism†

Dilute magnetic semiconductor oxides (DMSOs) hold great promise in bridging spintronics with semiconductor electronics, offering the potential for highly compact, high data-processing devices with reduced power consumption. Oxygen-deficient HfO₂ stands out among DMSOs due to its technologically important characteristics—large dielectric constant (κ ≅ 25), high refractive index (2.9) and excellent compatibility with CMOS technology. The origin of ferromagnetism in DMSOs, including HfO₂, is mainly attributed to oxygen vacancies. Two main strategies have been explored to enhance ferromagnetism in DMSOs: synthesizing low-dimensional nanostructures to increase oxygen vacancies via a high surface-to-volume ratio (i.e. a high specific surface area) and material doping with appropriate magnetic or non-magnetic ions to induce further vacancies within the lattice. The fabrication of doped 1D nanostructures combines both approaches to enhance ferromagnetism in DMSOs. To date, the fabrication of doped single-crystalline HfO₂ 1D nanostructures has remained elusive due to technical challenges. This work pioneers the fabrication of Ti-doped HfO₂ (i.e., Hf_1−xTi_xO₂; 0.01 ≤ x ≤ 0.50) 1D nanostructures with novel magnetic properties by using catalyst-assisted pulsed laser deposition. Increasing the Ti content is found to lead to shorter Hf_1−xTi_xO₂ 1D nanostructures, while, interestingly, the resulting magnetic properties show enhancement with increased Ti content, with Hf_1−xTi_xO₂ (10 at% Ti doping) exhibiting saturation magnetization nearly twice that of undoped HfO₂ nanowires. Given the high compatibility of Hf_1−xTi_xO₂ with CMOS technology and their critical temperature above room temperature, these novel nanostructures promise new applications in spintronic-CMOS integrated device technology.