Structural, magnetic and electronic properties of pulsed-laser-deposition grown SrFeO3-δ thin films and SrFeO3-δ /La2/3Ca1/3MnO3 multilayers

We studied the structural, magnetic and electronic properties of [Formula: see text] (SFO) thin films and [Formula: see text]/[Formula: see text] [Formula: see text]MnO₃ (LCMO) superlattices that have been grown with pulsed laser deposition (PLD) on [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] (LSAT) substrates. X-ray reflectometry and scanning transmission electron microscopy (STEM) confirm the high structural quality of the films and flat and atomically sharp interfaces of the superlattices. The STEM data also reveal a difference in the interfacial layer stacking with a SrO layer at the LCMO/SFO and a LaO layer at the SFO/LCMO interfaces along the PLD growth direction. The x-ray diffraction (XRD) data suggest that the as grown SFO films and SFO/LCMO superlattices have an oxygen-deficient [Formula: see text] structure with I4/ mmm space group symmetry ([Formula: see text]). Subsequent ozone annealed SFO films are consistent with an almost oxygen stoichiometric structure ([Formula: see text]). The electronic and magnetic properties of these SFO films are similar to the ones of corresponding single crystals. In particular, the as grown [Formula: see text] films are insulating whereas the ozone annealed films are metallic. The magneto-resistance effects of the as grown SFO films have a similar magnitude as in the single crystals, but extend over a much wider temperature range. Last but not least, for the SFO/LCMO superlattices we observe a rather large exchange bias effect that varies as a function of the cooling field.

Origin of the magnetic transition at 100 K in ε-Fe2O3 nanoparticles studied by x-ray absorption fine structure spectroscopy

The current study unveils the structural origin of the magnetic transition of the ε-Fe₂O₃ polymorph from an incommensurate magnetic order to a collinear ferrimagnetic state at low temperature. The high crystallinity of the samples and the absence of other iron oxide polymorphs have allowed us to carry out temperature-dependent x-ray absorption fine structure spectroscopy experiments out. The deformation of the structure is followed by the Debye-Waller factor for each selected Fe-O and Fe-Fe sub-shell. For nanoparticle sizes between 7 and 15 nm, the structural distortions between the Fe_te and Fe-D1_oc sites are localized in a temperature range before the magnetic transition starts. On the contrary, the inherent interaction between the other sub-shells (named Fe-O1,2 and Fe-Fe1) provokes cooperative magneto-structural changes in the same temperature range. This means that the Fe_te with Fe-D1_oc polyhedron interaction seems to be uncoupled with temperature dealing with these nanoparticle sizes wherein the structural distortions are likely moderate due to surface effects.

Epitaxial Growth of SrTiO3 Films on Cube-Textured Cu-Clad Substrates by PLD at Low Temperature Under Reducing Atmosphere

The growth of epitaxial {001}<100> SrTiO₃ (STO) on low-cost cube-textured Cu-based clad substrate at low temperature was carried out by means of pulsed laser deposition (PLD). STO film was deposited in one step under a reducing atmosphere (5% H₂ and 95% Ar mixture) to prevent the oxidation of the metal surface. The optimization of PLD parameters leads to a sharpest biaxial texture at a temperature as low as 500 °C and a thickness of 500 nm with a (100) STO layer. The upper limit of highly textured STO thickness was also investigated. The maximum thickness which retains the best quality {001}<100> texture is 800 nm, since the texture is preserved not only through the layer but also on the surface. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements showed that STO films are continuous, dense, and smooth with very low roughness (between 5 and 7 nm). This paper describes the development of STO layer by means of PLD in absence of oxygen throughout the process, suggesting an alternative and effective method for growing highly {001}<100> textured STO layer on low-cost metal substrates.

Competition between Polar and Nonpolar Lattice Distortions in Oxide Quantum Wells: New Critical Thickness at Polar Interfaces

Two basic lattice distortions permeate the structural phase diagram of oxide perovskites: antiferrodistortive (AFD) rotations and tilts of the oxygen octahedral network and polar ferroelectric modes. With some notable exceptions, these two order parameters rarely coexist in a bulk crystal, and understanding their competition is a lively area of active research. Here we demonstrate, by using the LaAlO_{3}/SrTiO_{3} system as a test case, that quantum confinement can be a viable tool to shift the balance between AFD and polar modes and selectively stabilize one of the two phases. By combining scanning transmission electron microscopy (STEM) and first-principles-based models, we find a crossover between a bulklike LaAlO_{3} structure where AFD rotations prevail, to a strongly polar state with no AFD tilts at a thickness of approximately three unit cells; therefore, in addition to the celebrated electronic reconstruction, our work unveils a second critical thickness, related not to the electronic properties but to the structural ones. We discuss the implications of these findings, both for the specifics of the LaAlO_{3}/SrTiO_{3} system and for the general quest towards nanoscale control of material properties.

Conserved gene regulation during acute inflammation between zebrafish and mammals

Zebrafish (Danio rerio), largely used as a model for studying developmental processes, has also emerged as a valuable system for modelling human inflammatory diseases. However, in a context where even mice have been questioned as a valid model for these analysis, a systematic study evaluating the reproducibility of human and mammalian inflammatory diseases in zebrafish is still lacking. In this report, we characterize the transcriptomic regulation to lipopolysaccharide in adult zebrafish kidney, liver, and muscle tissues using microarrays and demonstrate how the zebrafish genomic responses can effectively reproduce the mammalian inflammatory process induced by acute endotoxin stress. We provide evidence that immune signaling pathways and single gene expression is well conserved throughout evolution and that the zebrafish and mammal acute genomic responses after lipopolysaccharide stimulation are highly correlated despite the differential susceptibility between species to that compound. Therefore, we formally confirm that zebrafish inflammatory models are suited to study the basic mechanisms of inflammation in human inflammatory diseases, with great translational impact potential.

Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.

Abstract P2-08-31: Tumor and axillar downstaging as a prognostic factor and evaluation of effectiveness to primary chemotherapy in breast cancer: A retrospective analysis

Introduction: Evaluation of the benefit of primary chemotherapy (PC) is not easy to establish. Pathologic complete response (pCR) has been considered the main surrogate prognostic factor of patient's survival. However, patients achieving a pCR are not the only ones who benefit from PC. The purpose of our study is to find a measure of response that includes the maximum of patients that benefit from PC in terms of survival.

Patients and methods: 224 breast cancer patients were treated in Breast Cancer Unit from Institut Català d'Oncologia (ICO) L'Hospitalet with taxans and antracyclines-based PC +/- trastuzumab between 2009 and 2011. pCR was defined as no invasive carcinoma found in the tumor and in the axillary lymph nodes (ypT0/ypTis ypN0). Tumor and nodal downstaging (TNDS) was calculated according to the "neoadjuvant response index" (NRI) from Rodenhuis and also as a dichotomic variable: Positive includes those patients achieving dowstaging of both T and N plus T downstaging N0 and negatives those patients without downstaging in any of both variables. Those parameters were related to patient's overall survival (OS). Statistical analysis was performed with SPSS version 15.

Results: Median age 45.5 years (24-83). Main tumor characteristics: T2 (62.6%); N1 (50%); ductal infiltrating carcinoma (95.5%) and grade III (57.1%). Biological sub-type according to the last St Gallen classification: luminal A: 28 patients (pts); luminal B/Her2-: 61 pts; luminal B/HER2+: 34 pts; HER2+: 33 pts and triple negative: 69 pts. Pathologic complete response was achieved in 49 pts (22.5%). TNDS was evaluated in 181 patients and of those 90 was positive. According to NRI 74 patients presented cut-off&gt; 0.5 and 52 pts &gt; 0.7. Parameters related to OS were: biological subtype (P: 0.007); achieving a pCR (p: 0.007); NRI cut-off 0.5 (P: 0.001) and TNDS (p:0.000). In the multivariate analysis only TNDS and biological subtype remained statistically significant. When comparing those patients with positive vs. negative TNDS, the HR for recurrence was of 10.05 (IC 2.33 -43.57). The median OS of the series has not been reached. OS at 5y was 82.7% (IC: 77.1%-88%) and specific breast cancer OS at 5 y was 85% (IC:79.5%-90%). The number of events (breast cancer deaths) for each biological subtype according to positive vs. negative TNDS was: luminal A: 0/5 vs. 0/18; luminal B Her2-: 0/10 vs. 8/43; luminal B HER2+:0/23 vs. 2/9; HER2+: 0/22 vs. 0/2 and TN: 2/30 vs. 8/18. Survival data per subtypes and TNDS is immature due to the scarce number of events. Estimated 5y OS for TNDS positive vs. negative in luminal A: 100% vs. 100%; luminal B Her2-: 100% vs. 82%; luminal B HER2+:100 vs.77.7%; HER2+: 100% vs. 100% and TN: 93% vs. 55%, respectively.

Conclusion: In our series, TNDS measured either with the NRI from Rodenhuis or as a dichotomic variable was the best parameter to evaluate response to PC in terms of OS. OS of luminal A and luminal B/Her2 negative is less influenced by PC than the rest of subgroups. In fact both subgroups have good prognosis despite their poor sensitivity to chemotherapy. Those tumors that benefit most from PC were luminal B/ Her2+; Her2+ and triple negative patients who achieved a positive TNDS.

Citation Format: Falo C, Ventura LM, Petit A, Perez J, Cañellas J, Perez L, Loayza C, Gil M, Varela M, Garcia A, Pla MJ, Lopez A, Guma A, Pernas S. Tumor and axillar downstaging as a prognostic factor and evaluation of effectiveness to primary chemotherapy in breast cancer: A retrospective analysis. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-08-31.

Zebrafish Nk-lysins: First insights about their cellular and functional diversification

Nk-lysins are antimicrobial proteins produced by cytotoxic T lymphocytes and natural killer cells with a broad antimicrobial spectrum (including bacteria, fungi and parasites). Nevertheless, the implication of these proteins in the protection against viral infections is still poorly understood. In this work, four different Nk-lysin genes (nkla, nklb, nklc and nkld) were identified in the zebrafish genome. That means that zebrafish is the species with the higher repertoire of Nk-lysin genes described so far. The differential expression pattern of the Nk-lysins in several tissues, during ontogeny, among the different kidney cell populations, as well as between Rag1(-/-) and Rag1(+/+) individuals, could suggest a certain specialization of different cell types in the production of different Nk-lysin. Moreover, only two of these genes (nkla and nkld) were significantly up-regulated after viral infection, and this observation could be also a consequence of a functional diversification of the zebrafish Nk-lysins.

Bismuth labeling for the CT assessment of local administration of magnetic nanoparticles

Many therapeutic applications of magnetic nanoparticles involve the local administration of nanometric iron oxide based materials as seeds for magnetothermia or drug carriers. A simple and widespread way of controlling the process using x-ray computed tomography (CT) scanners is desirable. The combination of iron and bismuth in one entity will increase the atenuation of x-rays, offering such a possibility. In order to check this possibility core-shell nanocrystals of iron oxide@bismuth oxide have been synthesized by an aqueous route and stabilized in water by polyethylene glycol (PEG), and we have evaluated their ability to generate contrast by CT and magnetic resonance imaging (MRI) to measure the radiopacity and proton relaxivities using phantoms. High-resolution scanning transmission electron microscopy (STEM) revealed that the material consists of a highly crystalline 8 nm core of maghemite and a 1 nm shell of bismuth atoms either isolated or clustered on the nanocrystal's surface. The comparison of μCT and MRI images of mice acquired in the presence of the contrast shows that when local accumulations of the magnetic nanoparticles take place, CT images are more superior in the localization of the magnetic nanoparticles than MRI images, which results in magnetic field inhomogeneity artifacts.

Synthetic magnetoelectric coupling in a nanocomposite multiferroic

Given the paucity of single phase multiferroic materials (with large ferromagnetic moment), composite systems seem an attractive solution to realize magnetoelectric coupling between ferromagnetic and ferroelectric order parameters. Despite having antiferromagnetic order, BiFeO₃ (BFO) has nevertheless been a key material due to excellent ferroelectric properties at room temperature. We studied a superlattice composed of 8 repetitions of 6 unit cells of La_0.7Sr_0.3MnO₃ (LSMO) grown on 5 unit cells of BFO. Significant net uncompensated magnetization in BFO, an insulating superlattice, is demonstrated using polarized neutron reflectometry. Remarkably, the magnetization enables magnetic field to change the dielectric properties of the superlattice, which we cite as an example of synthetic magnetoelectric coupling. Importantly, controlled creation of magnetic moment in BFO is a much needed path toward design and implementation of integrated oxide devices for next generation magnetoelectric data storage platforms.

Insight into spin transport in oxide heterostructures from interface-resolved magnetic mapping

At interfaces between complex oxides, electronic, orbital and magnetic reconstructions may produce states of matter absent from the materials involved, offering novel possibilities for electronic and spintronic devices. Here we show that magnetic reconstruction has a strong influence on the interfacial spin selectivity, a key parameter controlling spin transport in magnetic tunnel junctions. In epitaxial heterostructures combining layers of antiferromagnetic LaFeO(3) (LFO) and ferromagnetic La(0.7)Sr(0.3)MnO(3) (LSMO), we find that a net magnetic moment is induced in the first few unit planes of LFO near the interface with LSMO. Using X-ray photoemission electron microscopy, we show that the ferromagnetic domain structure of the manganite electrodes is imprinted into the antiferromagnetic tunnel barrier, endowing it with spin selectivity. Finally, we find that the spin arrangement resulting from coexisting ferromagnetic and antiferromagnetic interactions strongly influences the tunnel magnetoresistance of LSMO/LFO/LSMO junctions through competing spin-polarization and spin-filtering effects.