Unexpected observation of spatially separated Kondo scattering and ferromagnetism in Ta alloyed anatase TiO2 thin films

Abstract

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.

The dramatic enhancement of ferromagnetism and band gap in Fe-doped In2O3 nanodot arrays

“…Since Dietl et al . theoretically predicted the room temperature (RT) ferromagnetism in Mn doped ZnO and GaN semiconductors via Zener’s p-d exchange model 2 , many efforts have been carried out on a series of transition metal (TM) elements doped wide-band-gap oxide semiconductors, such as ZnO 3–5 , TiO 2 6,7 , In 2 O 3 8–13 and SnO 2 14,15 . Among them, Fe-doped In 2 O 3 magnetic semiconductor is very attractive mainly due to its excellent electrical conductivity, high optical transparency, and high solubility of Fe ions in In 2 O 3 host lattice 9,11 .…”

Compensated thermal conductivity of metallically conductive Ta-doped TiO2

“…13 Degenerate Ta doping has been shown to induce high electrical conductivity and preserve high transmittances in the visible regime 14 and also realize the coexistence of ferromagnetism and Kondo scattering in this highly correlated electronic system in TiO 2 . 15 Herein, we report the concomitant electrical and thermal transport measurements in Ta-doped anatase TiO 2 thin films (Ta:TiO 2 ). The highest Ta doping reaches up to 5 at.…”

Kondo effect in magnetic tunnel junctions with an AlO x tunnel barrier

“…2(a), R * is negligible and exhibits no obvious change before temperature is decreased to about 40 K. Upon further reduction in temperature, R * begins to increase and becomes more significant as temperature continues to decrease. This behaviour presumably originates from the spin-exchange scattering interaction between the conduction electrons and the magnetic impurities, known as the Kondo effect [8,13]. …”