Heterostructures of strongly correlated oxides demonstrate various intriguingand potentially useful interfacial phenomena. LaMnO 3 /SrMnO 3 superlattices are presented showcasing a new high-temperature ferromagnetic phase with Curie temperature, T C ≈360 K, caused by electron transfer from the surface of the LaMnO 3 donor layer into the neighboring SrMnO 3 acceptor layer. As a result, the SrMnO 3 (top)/LaMnO 3 (bottom) interface shows an enhancement of the magnetization as depth-profiled by polarized neutron reflectometry. The length scale of charge transfer, λ TF ≈2 unit cells, is obtained from in situ growth monitoring by optical ellipsometry, supported by optical simulations, and further confirmed by high resolution electron microscopy and spectroscopy. A model of the inhomogeneous distribution of electron density in LaMnO 3 /SrMnO 3 layers along the growth direction is concluded to account for a complex interplay between ferromagnetic and antiferromagnetic layers in superlattices.

Epitaxial double perovskite La2CoMnO6 (LCMO) films were grown by metalorganic aerosol deposition on SrTiO3(111) substrates. A high Curie temperature, TC = 226 K, and large magnetization close to saturation, MS(5 K) = 5.8μB/f.u., indicate a 97% degree of B-site (Co,Mn) ordering within the film. The Co/Mn ordering was directly imaged at the atomic scale by scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDX). Local electron-energy-loss spectroscopy (EELS) measurements reveal that the B-sites are predominantly occupied by Co(2+) and Mn(4+) ions in quantitative agreement with magnetic data. Relatively small values of the (1/2 1/2 1/2) superstructure peak intensity, obtained by X-ray diffraction (XRD), point out the existence of ordered domains with an arbitrary phase relationship across the domain boundary. The size of these domains is estimated to be in the range 35-170 nm according to TEM observations and modelling the magnetization data. These observations provide important information towards the complexity of the cation ordering phenomenon and its implications on magnetism in double perovskites, and similar materials.

We report an atomic layer epitaxial growth of Ruddlesden-Popper (RP) thin films of SrO(SrTiO3)n (n = ∞, 2, 3, 4) by means of metalorganic aerosol deposition (MAD). The films are grown on SrTiO3(001) substrates by means of a sequential deposition of Sr-O/Ti-O2 atomic monolayers, monitored in-situ by optical ellipsometry. X-ray diffraction and transmission electron microscopy (TEM) reveal the RP structure with n = 2–4 in accordance with the growth recipe. RP defects, observed by TEM in a good correlation with the in-situ ellipsometry, mainly result from the excess of SrO. Being maximal at the film/substrate interface, the SrO excess rapidly decreases and saturates after 5–6 repetitions of the SrO(SrTiO3)4 block at the level of 2.4%. This identifies the SrTiO3 substrate surface as a source of RP defects under oxidizing conditions within MAD. Advantages and limitations of MAD as a solution-based and vacuum-free chemical deposition route were discussed in comparison with molecular beam epitaxy.

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Polarization‐dependent tip‐enhanced Raman spectroscopy (TERS) was carried out on double perovskite La2CoMnO6 (LCMO) thin films to determine the contributions of the enhancement by the excitation of surface plasmon polariton and tip‐induced polarization effects. Due to B‐site ordering and the resulting monoclinic P121/n1 structure, the spectra exhibit a strong Ag mode around 644 cm−1 originated from (Co/Mn)O6 stretching vibrations. The TERS contrast C, defined as the ratio of the total‐field (the sum of the near field and the far field) to the far‐field intensity, up to C ~60–110 for a cross‐polarized configuration (incident light polarization perpendicular to the detected one), reveals a possible breakdown of polarization‐dependent selection rules for the Raman scattering due to a tip‐induced near‐field depolarization component. We disentangled a significant enhancement for all observed modes in a parallel configuration with a TERS contrast of C ~2–5 due to general near‐field amplification, strongly affected also by the film thickness. With B‐site ordering and highly dielectric behavior, LCMO therefore provides an excellent test system to study TERS phenomena on oxide surfaces. Copyright © 2016 John Wiley & Sons, Ltd.