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Nonstoichiometry Driven Ferromagnetism in Double Perovskite La 2 Ni 1– x Mn 1+ x O 6 Insulating Thin Films

2019; American Chemical Society; Volume: 19; Issue: 5 Linguagem: Inglês

10.1021/acs.cgd.8b01897

1528-7505

Mónica Bernal-Salamanca, Z. Konstantinović, Ll. Balcells, Elisa V. Pannunzio-Miner, F. Sandiumenge, Laura López‐Mir, Bernat Bozzo, Javier Herrero‐Martín, A. Pomar, Carlos Frontera, B. Martı́nez,

Multiferroics and related materials

In this work we report on the epitaxial growth of La2NiMnO6 double perovskite thin films on top of (001) oriented SrTiO3 substrates by RF magnetron sputtering. The influence of oxygen pressure (PO2) and growth temperature on the microstructure, stoichiometry of the films, and magnetic and transport properties is thoroughly investigated. It is found that high oxygen pressure promotes the growth of stoichiometric films, with a Ni/Mn ratio almost equal to 1. However, these films exhibit poor ferromagnetic properties with respect to the expected optimum values corresponding to ferromagnetic ordering mediated by superexchange interaction between Mn4+ and Ni2+ according to the Goodenough-Kanamori rules. Most interestingly, films grown at low PO2 exhibit Ni/Mn ratios below 1, but ferromagnetic properties close to the optimal ones. The valence balance between Ni and Mn ions in nonstoichiometric sample has been elucidated by X-ray absorption spectroscopy. The results indicate that Ni deficiency plays a crucial role in the puzzling insulating ferromagnetic behavior observed in nonstoichiometric samples.