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We report the observation of spatially separated Kondo scattering and ferromagnetism in anatase Ta0.06Ti0.94O2 thin films as a function of thickness (10–200 nm). The Kondo behavior observed in thicker films is suppressed on decreasing thickness and vanishes below ~25 nm. In 200 nm film, transport data could be fitted to a renormalization group theory for Kondo scattering though the carrier density in this system is lower by two orders of magnitude, the magnetic entity concentration is larger by a similar magnitude and there is strong electronic correlation compared to a conventional system such as Cu with magnetic impurities. However, ferromagnetism is observed at all thicknesses with magnetic moment per unit thickness decreasing beyond 10 nm film thickness. The simultaneous presence of Kondo and ferromagnetism is explained by the spatial variation of defects from the interface to surface which results in a dominantly ferromagnetic region closer to substrate-film interface while the Kondo scattering is dominant near the surface and decreasing towards the interface. This material system enables us to study the effect of neighboring presence of two competing magnetic phenomena and the possibility for tuning them.

Controlling magnetic and magneto-optical properties of transparent metal oxide semiconductors has a significant potential for spintronics and photonics. Although ferromagnetism has been reported for several nanostructured transparent metal oxides in the absence of magnetic dopants, its origin and the nature of the exchange interactions remain controversial. Here, we report a variable-temperature−variable-field magnetic circular dichroism study of ZnO and SnO 2 nanocrystals prepared under oxidizing and reducing conditions. We observe the band splitting in ZnO and SnO 2 nanocrystals induced by localized doublet (S = 1/2) and triplet (S = 1) ground states, respectively. Photoluminescence measurements suggest that these states are associated with oxygen vacancies, either as isolated paramagnetic sites in ZnO or as local vacancy-based complexes in SnO 2 nanocrystals. The results of this work demonstrate the ability to tune carrier polarization in metal oxide nanocrystals by in situ control of the native defect formation and attest to the anomalous Zeeman splitting of the band states, which may play an important role in generating ferromagnetism in this class of materials.

Thin films of Ta incorporated TiO2 grown by pulsed laser deposition under specific growth conditions show room temperature ferromagnetism. Ta introduces carriers and concomitantly cationic defects, the combination of which leads to ferromagnetism. In this paper, we report on the dependence of the carrier and cationic defect density (compensation) on various parameters such as oxygen growth pressure, temperature and Ta concentration. Most likely, the Ti vacancies act as magnetic centers and the free electrons help with the exchange leading to ferromagnetism via Ruderman-Kittel-Kasuya-Yosida mechanism.

The design of photocatalysts with enhanced efficiency is pivotal to sustainable environmental remediation and renewable energy technologies. Simultaneous optimization of different factors affecting the performance of a photocatalyst, including the density of active surface sites, charge carrier separation, and valence and conduction band redox potentials, remains challenging. Here, we report the synthesis of ternary gallium tin oxide (GTO) nanocrystals (NCs) with variable composition and investigate the role of Ga3+ dopants in altering the electronic structure of rutile-type SnO2 NC lattice using steady-state and time-resolved photoluminescence spectroscopies. Substitutional incorporation of Ga3+ increases the band gap of SnO2 NCs, imparting the reducing power to the conduction band electrons, and causes the formation of acceptor states, which, in conjunction with electron trapping by donors (oxygen vacancies), leads to stabilization of the photoexcited carriers. Combination of a decrease in the charge recombination rate and adjustment of the conduction band reduction potential to more negative values synergistically promote the photocatalytic efficiency of the GTO NCs. The apparent rate constant for the photocatalytic degradation of rhodamine-590 dye by optimally prepared GTO NCs is 0.39 min–1, more than 2 times greater than that by benchmark AEROXIDE TiO2 P25 photocatalyst. The results of this work highlight the concept of using rational aliovalent doping of judiciously chosen metal oxide NC lattices to simultaneously manipulate multiple photocatalytic parameters, enabling the design of versatile and highly efficient photocatalysts.