Main researchers: Marta Gibert, Sara Catalano, Jennifer Fowlie, Claribel Dominguez

Rare-earth perovskite nickelates (RNiO3, R = Rare Earth) have been attracting the interest of the oxide community for many years, their properties coming from a strong degree of electron-lattice interaction. As the temperature is decreased, RNiO3 materials display a bandwidth-controlled Metal to Insulator Transition (MIT) to a unique ground state, characterized by a breathing distortion of the NiO6 units and an uncommon antiferromagnetic structure.

Due to the lack of reasonably sized single crystals of these compounds, high quality thin films represent an exceptional system for the study of the nickelates, allowing the tuning of their structural and electronic properties over an extended range.

In Geneva, we study high quality thin films of SmNiO3 and NdNiO3 as well as LaNiO3 (the only nickelate that has no MIT in bulk) deposited by RF off-axis magnetron sputtering.

In the past years, we have achieved control of the MIT and magnetic properties of these compounds through a variety of tools, such as strain, confinement, doping and heterostructuring [1],[2].

Currently, we have been studying the role of the growth direction and substrate symmetry on the NdNiO3 properties, focusing on the special clamping conditions provided by (111)pc oriented interfaces [3].

Phase Diagram of RNiO3.
Figure 1:Phase Diagram of the perovskite nickelates RNiO3 showing how the MIT and Néel Transitions can be tuned by cation size (in bulk) and by strain level (in thin films). Also shown is a comparison between (001) and (111) oriented interfaces.

LaNiO3, while always metallic in bulk, displays a metal to insulator transition as the thickness is reduced to few unit cells [4],[5]. In the ultrathin insulating regime, an antiferromagnetic order can be stabilized in the [111]-direction by interfacial coupling to the insulating ferromagnet LaMnO3, and used to generate interlayer magnetic coupling of a nature that depends on the exact number of LaNiO3 monolayers. For 7-monolayers-thick LaNiO3/LaMnO3 superlattices, negative and positive exchange bias as well as antiferromagnetic interlayer coupling between the LaMnO3 sublattices are observed as temperature increases [6],[7]. All three behaviours are explained based on the emergence of a (¼,¼,¼)-wavelength antiferromagnetic structure in LaNiO3, interfacial charge transfer and the presence of a structural asymmetry at the LaNiO3-LaMnO3 interfaces [8].

Figure 2: (111)-oriented (7 ML LaNiO3/7ML LaMnO3)15 superlattices. (a) Refectivities for circularly left (CL) and right (CR) polarized light measured at Mn L3-edge at 30 K and 0.05 T. Inset: extracted asymmetry ratio (CR-CL)/(CR+CL).(b) Sketch of the antiferromagnetic-coupled state between the LaMnO3 layers stabilized at T>30 K due to (c) the emergent (¼, ¼, ¼) spiral antiferromagnetic order induced in the ultrathin 7-monolayer-thick-[111]-LaNiO3 layers.

A few related publications:

[1] Electric-Field Control of the Metal-Insulator Transition in Ultrathin NdNiO3 Films
Raoul Scherwitzl, Pavlo Zubko, I. Gutierrez Lezama, Shimpei Ono, Alberto F. Morpurgo, Gustau Catalan and Jean- Marc Triscone
Advanced Materials 22, 5517 (2010).

[2] Electronic transitions in strained SmNiO3 thin films
S. Catalano, M. Gibert, V. Bisogni, O. E. Peil, F. He, R. Sutarto, M. Viret, P. Zubko, R. Scherwitzl, A. Georges, G. A. Sawatzky, T. Schmitt and J.-M. Triscone
APL Materials 2, 116110 (2014).

[3] Tailoring the electronic transitions of NdNiO3 films through (111)pc oriented interfaces
S. Catalano, M. Gibert, V. Bisogni, F. He, R. Sutarto, M. Viret, P. Zubko, R. Scherwitzl, G. A. Sawatzky, T. Schmitt and J.-M. Triscone
APL Materials 3, 062506 (2015).

[4] Metal-Insulator Transition in Ultrathin LaNiO3 Films
Raoul Scherwitzl, Stefano Gariglio, Marc Gabay, Pavlo Zubko, Marta Gibert, and Jean-Marc Triscone
Physical Review Letters 106, 246403 (2011).

[5] Electric-field tuning of the metal-insulator transition in ultrathin films of LaNiO3
Raoul Scherwitzl, Pavlo Zubko, Céline Lichtensteiger and Jean-Marc Triscone
Applied Physics Letters 95, 222114 (2009).

[6] Exchange bias in LaNiO3–LaMnO3 superlattices
Marta Gibert, Pavlo Zubko, Raoul Scherwitzl, Jorge Íñiguez and Jean-Marc Triscone
Nature Materials 11, 195-198 (2012).

[7] Interlayer coupling through a dimensionality-induced magnetic state
M. Gibert, M. Viret, P. Zubko, N. Jaouen, J.-M. Tonnerre, A. Torres-Pardo, S. Catalano, A. Gloter, O. Stephan and J.-M. Triscone Nature Communications 7, 11227 (2016).

[8] Interfacial control of magnetic properties at LaMnO3–LaNiO3 interfaces
M. Gibert, M. Viret, A. Torres-Pardo, C. Piamonteze, P. Zubko, N. Jaouen, J.-M. Tonnerre, A. Mougin, J. Fowlie, S. Catalano, A. Gloter, O. Stéphan and J.-M. Triscone
Nano Letters 15, 7355 - 7361 (2015).