A new hole-bridge structure based on a SiO2 nanoarray and its ferromagnetism

A simple and effective method to prepare a weakly ferromagnetic SiO2 nanoarray with a hole-bridge structure is described. The SiO2 nanospheres were prepared using a modified Stöber method. The array was obtained through three-dimensional self-organization from a SiO2 aqueous suspension by vertical deposition. Sintering makes the array more regular than the as-deposited state, and additional oxygen vacancies were produced during sintering. We obtained the hole-bridge structure by etching the sintered array using HF. Compared with other structures, the hole-bridge structure gives the largest magnetic signal at room temperature (0.016 ∼ emu/cm3). Oxygen vacancies in the SiO2 nanospheres are thought to be responsible in large measure for the ferromagnetism, and defects from the HF-etching make the SiO2 nanoarray with a hole-bridge structure show stronger ferromagnetic behavior.