Effect of oxygen partial pressure on the ferromagnetism of Cr-doped TiO₂films

Abstract

Polycrystalline Cr-doped TiO2 films were fabricated by co-sputtering Cr and TiO2 targets in a pure Ar and O2 mixture with various oxygen partial pressures. Ferromagnetism is observed in all samples and the Curie temperatures are well above 390 K. The saturation magnetization of films shows strong dependence on the oxygen growth pressure while keeping a constant Cr concentration. The ferromagnetism is enhanced in the films deposited at lower oxygen pressures which are thus oxygen deficient, indicating an important role of oxygen vacancies in the ferromagnetic origin of Cr-doped TiO2.

Anomalous Hall effect in sputter-deposited CoxTi1−xO2–δ films

“…The enhancement of ferromagnetism via growth of transition metal-doped TiO 2 in reduced atmosphere has been observed elsewhere [37]. Ferromagnetism in Cr-doped TiO 2 is reportedly induced by growth at lower oxygen pressure that induces oxygen vacancies [37]. Others have even reported ferromagnetism in reduced TiO 2 with no transition metal dopants [38][39][40], although this behavior for undoped material was not observed in the limited sample set considered in our study.…”

“…The appearance of magnetic behavior in both magnetization and Hall resistivity is consistent with a model in which magnetism in Co-doped TiO 2 anatase is a macroscopic property unrelated to precipitates, but the AHE does appear to correlate with growth conditions for which the formation of Ti n O 2nÀ1 defects is favored. The enhancement of ferromagnetism via growth of transition metal-doped TiO 2 in reduced atmosphere has been observed elsewhere [37]. Ferromagnetism in Cr-doped TiO 2 is reportedly induced by growth at lower oxygen pressure that induces oxygen vacancies [37].…”

Electronic Structure and Ferromagnetism Modulation in Cu/Cu2O Interface: Impact of Interfacial Cu Vacancy and Its Diffusion

“…However, the low Curie temperature far below room temperature impedes the DMS-based device development 5 . In recent years, oxides diluted magnetic semiconductors (ODMS), such as Fe-ZnO, Cr-TiO 2 , Mn-TiO 2 and etc, have attracted much attention due to their Curie temperature over 300 K in regards to DMS 6 7 8 . Unexpectedly, room temperature ferromagnetism (FM) has been observed in undoped oxides.…”

Magnetic Properties of N- and (Cr, N)-Doped TiO₂ Nanoparticles

“…In particular, nitrogen doping leads to the formation of oxygen vacancies (substitution of O with N) and thus to changes in the titanium oxidation sate (Ti 3+ ) and to the formation of exchanged coupled magnetic polarons [9,11]. For Cr-doping, the substitution of Cr 3+ for Ti 4+ into the TiO 2 lattice is usually found in these titanium dioxide nanostructures [12][13][14][15][16]. In this case within the framework of the BMP model, the magnetic exchange interaction between the oxygen vacancies and the magnetic impurities (Cr 3+ ) are invoked as the main origin of the room temperature ferromagnetism.…”