The complex interplay between superconducting and magnetic phases remains poorly understood. Here, we report on the phase separation of doped holes into separate magnetic and superconducting regions ...in superoxygenated La(2-x)Sr(x)CuO(4+y), with various Sr contents. Irrespective of Sr-doping, excess oxygen raises the superconducting onset to 40 K with a coexisting magnetic spin-density wave that also orders near 40 K in each of our samples. The magnetic region is closely related to the anomalous, 1/8-hole-doped magnetic versions of La(2)CuO(4), whereas the superconducting region is optimally doped. The two phases are probably the only truly stable ground states in this region of the phase diagram. This simple two-component system is a candidate for electronic phase separation in cuprate superconductors, and a key to understanding seemingly conflicting experimental observations.
In order to unambiguously identify the source of magnetism reported in recent studies of the Co-Te system, two sets of high-quality, epitaxial CoTex films (thickness ≈ 300 nm) were prepared by pulse ...laser deposition (PLD). X-ray diffraction (XRD) shows that all of the films are epitaxial along the 001 direction and have the hexagonal NiAs structure. There is no indication of any second phase metallic Co peaks (either fcc or hcp) in the XRD patterns. The two sets of CoTex films were grown on various substrates with PLD targets having Co:Te in the atomic ratio of 50:50 and 35:65. From the measured lattice parameters c = 5.396 Å for the former and c = 5.402 Å for the latter, the compositions CoTe1.71 (63.1% Te) and CoTe1.76 (63.8% Te), respectively, are assigned to the principal phase. Although XRD shows no trace of metallic Co second phase, the magnetic measurements do show a ferromagnetic contribution for both sets of films with the saturation magnetization values for the CoTe1.71 films being approximately four times the values for the CoTe1.76 films. 59Co spin-echo nuclear magnetic resonance (NMR) clearly shows the existence of metallic Co inclusions in the films. The source of weak ferromagnetism reported in several recent studies is due to the presence of metallic Co, since the stoichiometric composition “CoTe” does not exist.
Resistivity and resistance measurements have been carried out for thin films of cryptomelane‐type manganese oxide (OMS‐2) grown onto (001), (110), and (111)STO single crystals substrates via pulsed ...laser deposition. While the symmetries of the (001) and (111)STO substrate surfaces give deposits consisting of multiple nanofiber arrays with isotropic in‐plane resistivities, only a single nanofiber array is formed on (110)STO giving highly anisotropic electrical properties with very low resistivity values measured parallel to the fibers and similar to the lowest value ever reported.
Inelastic neutron scattering has been used to study the in-plane Cu-O bond-stretching mode in oxygen-doped La1.94Sr0.06CuO4.035 (Tc=38K) and La2CuO4+δ (Tc=43K). Similar to results from optimally ...doped La1.85Sr0.15CuO4 (Tc=35K), we observe anomalous features in the dispersion of this half-breathing mode in the form of a softening halfway through the Brillouin zone. Considering the differences in electronic structure and local environment between the oxygen- and strontium-doped compounds with similar Tc, we rule out a connection between the phonon anomaly and structural instabilities related to the specific dopant type. We interpret the phonon anomaly as a signature of correlated charge fluctuations ubiquitous in optimally doped superconductors.
Cryptomelane-type manganese oxide (OMS-2) has been widely used to explore the semiconducting and catalytic properties of molecular sieves with mixed-valent frameworks. Selective synthesis of ...patterned thin films of OMS-2 with hierarchical nanostructures and oriented crystals is challenging owing to difficulties in preserving the mixed valence, porosity and crystalline phase. Here, we report that pulsed-laser ablation of OMS-2 in an oxygen-rich medium produces a three-dimensional nanostructured array of parallel and inclined OMS-2 fibres on bare substrates of (001) single-crystal strontium titanate. Both parallel and inclined OMS-2 fibres elongate along the 001(OMS-2) direction. The parallel fibres interact strongly with the substrate and grow epitaxially along (STO) with lattice misfits of less than 4%, whereas the inclined fibres are oriented with (301) parallel to the substrate surface. The spontaneous orientation of the crystalline OMS-2 domains over the STO surface opens up a new avenue in lattice-engineered synthesis of multilayer materials.
Bulk Scandium trifluoride (\(\mathrm{ScF_3}\)) is known for a pronounced negative thermal expansion (NTE) over a wide range of temperature, from \(10~\mathrm{K}~\text{to}~ 1100~\mathrm{K}\). The ...structure of \(\mathrm{ScF_3}\) can be described as an \(\mathrm{ABX_3}\) perovskite with an empty A-site and a space group of Pm-3m. Growing thin films of \(\mathrm{ScF_3}\) allows for tuning the lattice constant, the thermal expansion, and the construction of devices based upon differential thermal expansion. We have investigated the growth of \(\mathrm{ScF_3}\) films on oxide and fluoride substrates using pulsed laser deposition (PLD) This letter describes the successful growth recipe for producing high quality epitaxial \(\mathrm{ScF_3}\) thin films on positive thermal expansion (PTE) lithium fluoride (\(\mathrm{LiF}\)) substrates, at substrate temperature, \(350^{\circ}\mathrm{C}\) with a laser repetition rate of \(1~\mathrm{Hz}\), with an energy per pulse of \(600~\mathrm{mJ}\), under a vacuum of \(1.5\times 10^{-6}~ \mathrm{torr}\), for a growth time of \(6\) hours. However, even for films with excellent epitaxy and sharp peaks along the principal axes, diffraction peaks from certain crystallographic directions are extremely broad, with the example of (\(104\)) reflections, in this work. We attribute this broadening to disorder in the \(\mathrm{F_6}\) octahedral rotations that occur as an attempt to accommodate the large temperature-induced lattice mismatch that results in cooling from the growth temperature for this system of a NTE film mated to a PTE substrate.
Inelastic neutron scattering has been used to study the in-plane Cu-O bond-stretching mode in oxygen doped La\(_{1.94}\)Sr\(_{0.06}\)CuO\(_{4.035}\) (\(T_c = 38\,\text{K}\)) and ...La\(_2\)CuO\(_{4+\delta}\) (\(T_c = 43\,\text{K}\)). Similar to results from optimally doped La\(_{1.85}\)Sr\(_{0.15}\)CuO\(_4\) (\(T_c = 35\,\text{K}\)), we observe anomalous features in the dispersion of this half-breathing mode in the form of a softening halfway through the Brillouin Zone. Considering the differences in electronic structure and local environment between the oxygen- and strontium-doped compounds with similar \(T_\text{c}\), we rule out a connection between the phonon anomaly and structural instabilities related to the specific dopant type. We interpret the phonon anomaly as a signature of correlated charge fluctuations possibly connected to stripes.
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