Oxygen vacancy-induced room-temperature ferromagnetism in D-D neutron irradiated single-crystal TiO₂ (001) rutile

Remarkable room temperature ferromagnetism in pure single-crystal rutile TiO₂ (001) samples irradiated by D-D neutron has been investigated. By combining X-ray diffraction and positron annihilation lifetime, the contracted lattice has been clearly identified in irradiated TiO₂, where Ti⁴⁺ ions can be easily reduced to the state of Ti³⁺. As there were no magnetic impurities that could contaminate the samples during the whole procedure, some Ti³⁺ ions reside on interstitial or substituted sites accompanied by oxygen vacancies should be responsible for the ferromagnetism.