Electrical transport properties and Kondo effect in La1\u2212xPrxNiO3\u2212\u03b4thin films

Van Hien-Hoang,Heon-Jung Kim,Nak-Kwan Chung

doi:10.1038/s41598-021-84736-2

Van Hien-Hoang, Heon-Jung Kim + Show 1 more

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https://doi.org/10.1038/s41598-021-84736-2

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Abstract

The Kondo effect has been a topic of intense study because of its significant contribution to the development of theories and understanding of strongly correlated electron systems. In this work, we show that the Kondo effect is at work in La1−xPrxNiO3−δ (0 ≤ x ≤ 0.6) thin films. At low temperatures, the local magnetic moments of the 3d eg electrons in Ni2+, which form because of oxygen vacancies, interact strongly with itinerant electrons, giving rise to an upturn in resistivity with x ≥ 0.2. Observation of negative magnetoresistance, described by the Khosla and Fisher model, further supports the Kondo picture. This case represents a rare example of the Kondo effect, where Ni2+ acts as an impurity in the background of Ni3+. We suggest that when Ni2+ does not participate in the regular lattice, it provides the local magnetic moments needed to scatter the conduction electrons in the Kondo effect. These results offer insights into emergent transport behaviors in metallic nickelates with mixed Ni3+ and Ni2+ ions, as well as structural disorder.

Highlights

The Kondo effect has been a topic of intense study because of its significant contribution to the development of theories and understanding of strongly correlated electron systems
All film peaks were located on the right side of the corresponding STO (00l) peak, meaning that the out-of-plane lattice parameter cfilm of the L a1−xPrxNiO3−δ (LPNO) layer was smaller than that of the STO substrate
For a more detailed comparison, we present the difference in curves between the experimental data and the theoretical curves based on the Kondo effect and the electron interaction (EEI) effect (Fig. 4b) for the sample with x = 0.2

Summary

Introduction

The Kondo effect has been a topic of intense study because of its significant contribution to the development of theories and understanding of strongly correlated electron systems. The Kondo effect was first discovered in conventional metals containing small concentrations of magnetic impurities, recent studies suggest its existence in several oxides and carbon-based materials such as S rTiO32, graphene[3], doped T iO2 thin films[4], etc These observations have inspired important further development and refinements of the Kondo physics. When its thickness is reduced below 7 unit cells (u.c.) to an ultrathin LNO, a temperaturedriven MIT has been observed[7] Another RNiO3 (R = Pr, Nd, Sm, Eu) is orthorhombic with a Pbnm space group in the high-temperature metallic phase, and its structure becomes monoclinic with P21/n in the low-temperature insulating p hase[8]. The ground state of the paramagnetic state is more adequately described as a d8L configuration (where L denotes a ligand hole)[15]

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