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arXiv · 2112.10076

The origin of insulating and non-ferromagnetic SrRuO3 monolayers

Zeeshan Ali·Zhen Wang·Andrew O'Hara·Mohammad Saghayezhian·Donghan Shin·Yimei Zhu·Sokrates T. Pantelides·Jiandi Zhang
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Abstract

The electro-magnetic properties of ultrathin epitaxial ruthenate films have long been the subject of debate. Here we combine experimental with theoretical investigations of (SrTiO3)5-(SrRuO3)n-(SrTiO3)5 (STO5-SROn-STO5) heterostructures with n = 1 and 2 unit cells, including extensive atomic-resolution scanning-transmission-electron-microscopy imaging, electron-energy-loss-spectroscopy chemical mapping, as well as transport and magneto-transport measurements. The experimental data demonstrate that the STO5-SRO2-STO5 heterostructure is stoichiometric, metallic, and ferromagnetic with TC ~ 128 K, even though it lacks the characteristic bulk-SRO octahedral tilts and matches the cubic STO structure. In contrast, the STO5-SRO1-STO5 heterostructure features Ru-Ti intermixing in the RuO2 layer, also without octahedral tilts, but is accompanied by a loss of metallicity and ferromagnetism. Density-functional-theory calculations show that stoichiometric n = 1 and n = 2 heterostructures are metallic and ferromagnetic with no octahedral tilts, while non-stoichiometry in the Ru sublattice in the n = 1 case opens an energy gap and induces antiferromagnetic ordering. Thus, the results indicate that the observed non-stoichiometry is the cause of the observed loss of metallicity and ferromagnetism in the n = 1 case.

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Zeeshan Ali, Zhen Wang, Andrew O'Hara, Mohammad Saghayezhian, Donghan Shin, Yimei Zhu, Sokrates T. Pantelides, Jiandi Zhang. 2021-12-19. The origin of insulating and non-ferromagnetic SrRuO3 monolayers. https://doi.org/10.1103/physrevb.105.054429

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