Room-temperature ferromagnetism observed in alumina films

We have prepared alumina thin films on Si substrates using a radio frequency (RF) sputtering method, and have observed room-temperature ferromagnetism (RTFM) in the thin films. When the thin films were annealed in vacuum, the saturation magnetization (Ms) increased, while annealing the sample in the air contributed to a decrease in the value of Ms. The Ms of the thin film also decreased as the thickness increased. We confirm that the unpaired electron spins responsible for ferromagnetism (FM) in Al2O3−δ thin films have their origin in the oxygen vacancies, especially at the interface of the Al2O3−δ thin film and the Si substrate.

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