Observations of the Kondo effect and its coexistence with ferromagnetism in a magnetically undoped metal oxide nanostructure

Abstract

In this work, we report unusual observations of Kondo effect and coexistence of Kondo effect and ferromagnetism in Indium Tin Oxide (ITO) nanowires that were synthesized without incorporating any magnetic impurities. The temperature-dependent resistivity (ρ-T) data exhibited an upturn below 80 K and then tended to saturate below 10 K. The ρ-T and magnetoresistance data were analyzed using the n-channel Kondo model, and from the obtained values of S = 1 and n ~ 1, the nanowires were expected to be an under-screened Kondo system. A model was also proposed to explain the formation of localized S = 1 spin centers in the ITO nanowires. This work could provide insights into the understanding of spin-related novel phenomena in metal oxide nanostructures.

A Josephson phase battery

“…( 2) when h → −h, whereas the observed hysteretic behavior suggests a ferromagnetic coupling between the magnetic impurities in the nanowire. At low temperatures, the coexistence of Kondo and ferromagnetism is not unusual [39] and well describes the hysteretic nonmonotonic behavior observed in ϕ tot (B y ). Indeed, due to the antiferromagnetic nature of the Kondo interaction, the effective exchange field created by these unpared spins is opposite to the Zeeman field generated by B y so that the two contributions are competing in the anomalous phase with a partial cancellation.…”

“…From the fit we deduced a density of magnetic impurities of ∼ 4 ppm (see SI for more details on the fitting procedure). The presence of these unpaired spins can be ascribed to the nanowire surface oxides, as already observed in undoped metal oxide nanostructures [38,39], even if defects in the nanowire crystalline structure [40] cannot be excluded a priori. Although, the amount of intrinsic magnetic impurities is not fully controllable, their presence is crucial for the operation and implementation of the phase battery, as discussed below.…”

Spin-Split Band Hybridization in Graphene Proximitized with α-RuCl3 Nanosheets

“…These emerge already prior to the actual antiferromagnetic ordering at about 7 K, and hence may influence the electrical conductivity in this temperature range. 33 We note that both the dramatic drop in resistance as well as the upturn of the resistance at low temperature are generic and have been observed in all investigated devices. By contrast, the resistance feature in the gate voltage-dependent traces of panel b around V g = +20 V did not appear in all devices (see, for example, additional data on device D2 in SI).…”

“…One possible explanation for the resistance minimum observed in the resistance versus temperature dependence (Figure c) relates to spin flip events in the α-RuCl 3 . These emerge already prior to the actual antiferromagnetic ordering at about 7 K, and hence may influence the electrical conductivity in this temperature range . We note that both the dramatic drop in resistance as well as the upturn of the resistance at low temperature are generic and have been observed in all investigated devices.…”

Electron-electron interactions in nano-patterned La0.3Sr0.7MnO3 thin films

“…Here the resistivity upturn is due to an interaction between localized magnetic impurities and conduction electrions 36 . A wide variety of materials have been shown to exhibit the Kondo effect including dilute magnetic alloys 37 , magnetic semiconductors 38 , quantum dots 39 and most recently even non-magnetic materials without magnetic impurities 40 . In the devices considered here, however it seems unlikely that the Kondo effect could play a role because LSMO does not a priori contain localized magnetic impurities.…”