Single Crystals Of La1 Research Articles

Structure and magnetic properties of a La0.75Sr0.25Cr0.90O[formula omitted] single crystal

We have successfully grown large and good-quality single crystals of the La0.75Sr0.25Cr0.90O3−δ compound using the floating-zone method with laser diodes. We investigated the crystal quality, crystallography, chemical composition, magnetic properties and the oxidation state of Cr in the grown single crystals by employing a combination of techniques, including X-ray Laue and powder diffraction, scanning electron microscopy, magnetization measurements, X-ray photoelectron spectroscopy and light absorption. The La0.75Sr0.25Cr0.90O3−δ single crystal exhibits a single-phase composition, crystallizing in a trigonal structure with the space group R3̄c at room temperature. The chemical composition was determined as La0.75Sr0.25Cr0.90O3−δ, indicating a significant chromium deficiency. Upon warming, we observed five distinctive characteristic temperatures, namely T1=21.50(1) K, T2=34.98(1) K, T3=117.94(1) K, T4=155.01(1) K, and TN=271.80(1) K, revealing five distinct magnetic anomalies. Our magnetization study allows us to explore the nature of these anomalies. Remarkably, the oxidation state of chromium in the single-crystal La0.75Sr0.25Cr0.90O3−δ, characterized by a band gap of 1.630(8) eV, is exclusively attributed to Cr3＋ ions, making a departure from the findings of previous studies on polycrystalline materials.

Structure and properties of La0.6Ce0.3Pr0.1B6‐ZrB2, a directionally solidified eutectic with different growth rates

AbstractLa0.6Ce0.3Pr0.1B6‐ZrB2, a directionally solidified eutectic (DSE), is a material with a high‐performance thermionic emission with great application prospects. The influence of the growth rates of this DSE on the microstructure, growth direction, two phases orientation relationship, mechanical properties, and thermionic emission properties was investigated. The experimental results show that the microstructure and growth direction of the two phases varied with the growth rate of the eutectic: the faster the growth rate, the lower the uniformity of the ZrB2 phase became, and the growth directions of the La0.6Ce0.3Pr0.1B6 matrix and the ZrB2 phase were also altered accordingly. In the La0.6Ce0.3Pr0.1B6‐ZrB2 DSE with a growth rate of 100 mm/h, the two phases have a unique growth direction and a crystallographic orientation relationship. The fracture toughness of the La0.6Ce0.3Pr0.1B6‐ZrB2 DSE is at least 50% higher than that of the single crystal La0.6Ce0.3Pr0.1B6, and the fracture toughness of the DSEs formed at different growth rates also differed.

Parallel spin stripes and their coexistence with superconducting ground states at optimal and high doping in La1.6−xNd0.4SrxCuO4

Three-dimensional, commensurate long-range magnetic order in La2CuO4 quickly evolves to quasi-two-dimensional, incommensurate correlations upon doping with mobile holes, and superconductivity follows for x as small as 0.05 in the La2−xSrx/BaxCuO4 family of superconductors. The onset of superconductivity in these systems is known to be coincident with a remarkable rotation of the incommensurate spin order from “diagonal stripes” below x = 0.05 to “parallel stripes” above. However, little is known about the spin correlations at optimal and high doping levels, around and beyond the proposed quantum critical point for the pseudogap phase, p*. Here, we present elastic and inelastic neutron scattering measurements on single crystals of La1.6−xNd0.4SrxCuO4 with x = 0.125, 0.19, 0.24, and 0.26 and show that two-dimensional, quasistatic, parallel spin stripes have an onset at temperatures such that the parallel spin stripe phase extends beyond p* and envelops the entirety of superconducting ground states in this system. We also show that the elastic order parameter for parallel spin stripes at optimum doping, x = 0.19, displays an inflection point at superconducting Tc, while the low-energy dynamic spectral weight of parallel stripe fluctuations grows with decreasing temperature and saturates below Tc.3 MoreReceived 2 September 2020Revised 12 March 2021Accepted 29 April 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.023151Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasSuperconductivityPhysical SystemsCupratesHigh-temperature superconductorsTechniquesNeutron scatteringCondensed Matter, Materials & Applied Physics

Spectroscopic characterization of electronic structures of ultra-thin single crystal La0.7Sr0.3MnO3

We have successfully fabricated high quality single crystalline La0.7Sr0.3MnO3 (LSMO) film in the freestanding form that can be transferred onto silicon wafer and copper mesh support. Using soft x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) spectroscopy in transmission and reflection geometries, we demonstrate that the x-ray emission from Mn 3s-2p core-to-core transition (3sPFY) seen in the RIXS maps can represent the bulk-like absorption signal with minimal self-absorption effect around the Mn L3-edge. Similar measurements were also performed on a reference LSMO film grown on the SrTiO3 substrate and the agreement between measurements substantiates the claim that the bulk electronic structures can be preserved even after the freestanding treatment process. The 3sPFY spectrum obtained from analyzing the RIXS maps offers a powerful way to probe the bulk electronic structures in thin films and heterostructures when recording the XAS spectra in the transmission mode is not available.

Relativistic Ginzburg–Landau equation: An investigation for overdoped cuprate films

By introducing the imaginary time, Gor'kov's Ginzburg–Landau equation at zero temperature can be extended to an exact relativistic form without any phenomenological parameter, which is intended to describe the zero-temperature overdoped cuprate. By using such a relativistic equation, we have shown that the two-class scaling observed in the overdoped side of single-crystal La2−xSrxCuO4 (LSCO) films (Božović (2016) [7]) can be derived exactly. In this paper, we further test the validity of the relativistic Ginzburg–Landau equation. By applying the perturbation method into this equation, we theoretically predict that near the superconductor–metal transition point in the overdoped side of LSCO films, the zero-temperature correlation length ξ(0) and the transition temperature Tc should yield a novel scaling ξ(0)∝Tc−σ with a critical exponent σ≈1.31 (up to the two-loop approximation). Here, we propose a diffraction experiment between X-rays and zero-temperature LSCO films to measure the critical exponent σ.

Description of the Colossal Magnetoresistance of La1.2Sr1.8Mn2O7 Based on Spin-Polaron and Orientation Conductivity Mechanisms in the Paramagnetic Temperature Region

The resistance of single-crystal La1.2Sr1.8Mn2(1 – z)O7 is studied experimentally and theoretically in the 75–300 K temperature range in magnetic fields varying in intensity from 0 to 90 kOe. The magnetoresistance is governed by spin-polaron and orientation conductivity mechanisms. The observed magnetoresistance of La1.2Sr1.8Mn2O7 at 75–300 K is characterized using the method of separation of contributions from different conductivity mechanisms. The calculated and experimental data agree closely. Temperature dependences of the spin-polaron size (in relative units) are calculated in the 75–300 K interval in zero magnetic field and in a 90 kOe field. It is demonstrated that the increasing (along the magnetic field) spin-polaron linear size gives rise to colossal magnetoresistance. In other words, the size change of magnetic inhomogeneities produces the primary contribution to the colossal magnetoresistance value.

Synthesis of single-crystal La0.67Sr0.33MnO3 freestanding films with different crystal-orientation

We report the synthesis of single-crystal La0.67Sr0.33MnO3 (LSMO) freestanding films with different crystal orientations. By using pulsed laser deposition, water soluble perovskite-like sacrificial layers Sr3Al2O6 (SAO) followed by LSMO films are grown on differently oriented SrTiO3 substrates. Freestanding LSMO films with different orientations are obtained by etching the SAO in pure water. All the freestanding films show room-temperature ferromagnetism and metallicity, independent of the crystal orientation. Intriguingly, the Curie temperature (TC) of the freestanding films is increased due to strain relaxation after releasing from the substrates. Our results provide an additional degree of freedom to tailor the properties of freestanding perovskite oxide heterostructures by crystal orientation and an opportunity to further integrate different oriented films together.

Inhomogeneous-strain-induced magnetic vortex cluster in one-dimensional manganite wire

Mixed-valance manganites with strong electron correlation exhibit strong potential for spintronics, where emergent magnetic behaviors, such as propagation of high-frequency spin waves and giant topological Hall Effects can be driven by their mesoscale spin textures. Here, we create magnetic vortex clusters with flux closure spin configurations in single-crystal La0.67Sr0.33MnO3 wire. A distinctive transformation from out-of-plane domains to a vortex state is directly visualized using magnetic force microscopy at 4 K in wires when the width is below 1.0 μm. The phase-field modeling indicates that the inhomogeneous strain, accompanying with shape anisotropy, plays a key role for stabilizing the flux-closure spin structure. This work offers a new perspective for understanding and manipulating the non-trivial spin textures in strongly correlated systems.

Dielectric Parameters of Elastically Strained Heteroepitaxial SrTiO3 Films

Three-layer epitaxial SrRuO3/SrTiO3/SrRuO3 heterostructures with the 900-nm-thick intermediate layer of strontium titanate have been grown on single-crystal (001)La0.29Sr0.71Al0.65Ta0.35O3 substrates by the laser evaporation method. Plane-parallel film capacitors have been formed on the basis of the grown heterostructures using photolithography and ion etching. Temperature dependences of the dissipation factor have been measured for these capacitors at different bias voltages applied to strontium ruthenate electrodes. Temperature dependences of the permittivity of the intermediate SrTiO3 layer in the formed capacitor structures are visualized with compensation of the internal electric field and without it. The reasons for the sharp increase in the dielectric loss in the formed film capacitors at temperatures below 50 K are analyzed.

The Vanishing Superfluid Density in Cuprates—and Why It Matters

Recently, we have released the results of a comprehensive study of a couple thousand single-crystal La2−xSrxCuO4 films, covering densely the entire overdoped side of the phase diagram (Božovic et al. Nature 536, 309–311, 2016; Wu et al. Nature 547, 432–435, 2017). Here, we review the key experimental findings, place them in the context of other important well-established facts and observations, and discuss their implications for our understanding of high-temperature superconductivity in cuprates. We conclude that it involves some new physics that requires going beyond the standard Fermi liquid description of the normal state and Bardeen-Cooper-Schrieffer description of the superconducting state.

Thermal Conductivity: Glass‐Like Through‐Plane Thermal Conductivity Induced by Oxygen Vacancies in Nanoscale Epitaxial La0.5Sr0.5CoO3−δ (Adv. Funct. Mater. 47/2017)

In article 1704233, Xiaojia Wang and co-workers demonstrate that single crystal La0.5Sr0.5CoO3−δ films possess a glass-like thermal conductivity through their plane. A combination of oxygen vacancies, Sr distribution, size effect, and weak electron/phonon coupling causes this effect. This discovery opens possibilities for tuning the thermal properties of perovskite thin films by manipulating heat carriers via structural/defect engineering at the atomic level.

Direct and real time probe of photoinduced structure transition in colossal magnetoresistive material

We report a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. The fast process is designated as the initial melting of orthorhombic phase induced by the Mn-O bond change that is most likely driven by the quenching of the dynamic Jahn-Teller distortion following the photo-excitation. The slow process is attributed to the growing of newly formed structure domain from the photo-excited sites to the neighboring non-excited orthorhombic sites.

Ultrafast Jahn–Teller polaron dynamics in a bi‐layered manganite single crystal

We report the photoinduced ultrafast quasiparticle recombination dynamics of colossal magnetoresistance single crystal La1.2Sr1.8Mn2O7 by using femtosecond time‐resolved reflection spectroscopy in a wide range of temperatures. Here, we find the transient reflectivity change ΔR exhibits a competition process of a fast negative component (∼ sub‐picosecond) against a slow positive component (∼ nanosecond), as the sample goes from paramagnetic (PM) to ferromagnetic (FM) state with decreasing the temperature. The very fast initial decay of the photoinduced ΔR corresponds to the photoionization of the Jahn–Teller polaronic response, which is unambiguously sensitive to the coupling between electron and lattice in the PM and FM phases in La1.2Sr1.8Mn2O7 single crystal. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Evidence of weak localization in quantum interference effects observed in epitaxial La0.7Sr0.3MnO3 ultrathin films.

Quantum interference effects (QIEs) dominate the appearance of low-temperature resistivity minimum in colossal magnetoresistance manganites. The T1/2 dependent resistivity under high magnetic field has been evidenced as electron-electron (e-e) interaction. However, the evidence of the other source of QIEs, weak localization (WL), still remains insufficient in manganites. Here we report on the direct experimental evidence of WL in QIEs observed in the single-crystal La0.7Sr0.3MnO3 (LSMO) ultrathin films deposited by laser molecular beam epitaxy. The sharp cusps around zero magnetic field in magnetoresistance measurements is unambiguously observed, which corresponds to the WL effect. This convincingly leads to the solid conclusion that the resistivity minima at low temperatures in single-crystal manganites are attributed to both the e-e interaction and the WL effect. Moreover, the temperature-dependent phase-coherence length corroborates the WL effect of LSMO ultrathin films is within a two-dimensional localization theory.

Single crystal growth and characterization of NaxLn1−xMoO4, Ln=La, Ce, Pr, Nd, Sm, and Eu (x=0.397–0.499)

Single crystals of La0.516(3)Na0.484(3)MoO4, Ce0.512(2)Na0.488(2)MoO4, Pr0.502(2)Na0.498(2)MoO4, Nd0.501(2)Na0.499(2)MoO4, Sm0.509(2)Na0.491(2)MoO4, and Eu0.603(2)Na0.397(2)MoO4 were grown for the first time out of an alkali metal halide eutectic flux. All compounds crystallize in the tetragonal space group I41/a. UV/Vis measurements show the presence of an absorption edge for all compounds except Eu0.603(2)Na0.397(2)MoO4. The temperature dependence of the magnetic susceptibility was measured for all compounds and found to be paramagnetic across the entire 2–300K temperature range measured.

An electron spin resonance study of Eu doping effect in La4/3Sr5/3Mn2O7 single crystal

The effect of Eu3+ ion doping in the La sites of single-crystal La4/3Sr5/3Mn2O7 was investigated. Electron spin resonance (ESR) was applied to La4/3Sr5/3Mn2O7 and (La0.8Eu0.2)4/3Sr5/3Mn2O7 single crystals. A phase separation and phase transitions were observed from the ESR spectra data. Between 350 K and 300 K, both paramagnetic resonance (PMR) and anisotropic ferromagnetic resonance (FMR) lines were observed in the ab plane and the c axis direction, suggesting a coexistence of the paramagnetic (PM) phase and the ferromagnetic (FM) phase. The magnetization measurement reveals a spin-glass-like behavior in single-crystal (La0.8Eu0.2)4/3Sr5/3Mn2O7 below the temperature of spin freezing Tf (∼ 29.5 K).

Angle and frequency dependence of self-energy from spin fluctuation mediated d-wave pairing for high temperature superconductors

We investigated the characteristics of spin fluctuation mediated superconductivity employing the Eliashberg formalism. The effective interaction between electrons was modeled in terms of the spin susceptibility measured by inelastic neutron scattering experiments on single crystal La2−xSrxCuO4 superconductors. The diagonal self-energy and off-diagonal self-energy were calculated by solving the coupled Eliashberg equation self-consistently for the chosen spin susceptibility and tight-binding dispersion of electrons. The full momentum and frequency dependence of the self-energy is presented for optimally doped, overdoped, and underdoped LSCO cuprates in a superconductive state. These results may be compared with the experimentally deduced self-energy from ARPES experiments.

Elastic and magnetic properties of single-crystal La0.4Pr0.3Ca0.3MnO0.3

Elastic and magnetic properties of single-crystal La0.4Pr0.3Ca0.3MnO0.3

Magnetocaloric effect in inhomogeneous ferromagnets

The article is devoted to the theoretical study of magnetocaloric effect in imhomogeneous ferromagnets in vicinity of magnetic phase transitions of first and second orders as well as in vicinity of tricritical and critical points. In the frame of Landau theory the formulae for the magnetic field induced entropy change are derived. The theory is compared with the experimental data obtained on single crystals of La0.7Ba0.3MnO3 (second order transition) and La0.7Ca0.3MnO3 (first order transition).

Single-crystal rare earths manganites La1−x−yBixAyMnαO3±β (A = Ba, Pb): Crystal structure, composition, and Mn ions valence state. X-ray diffraction and XPS study

Single crystals of La1−xBixMnαO3±β and La1−x−yBixAyMnαO3±β (A=Ba, Pb) are grown, their crystal and electron structure is studied. Relative Mn3+/Mn4+ abundance in each single crystal is determined via fitting experimental Mn2p-spectra with weighted superposition of theoretical spectra of tri- and quadrivalent Mn, and, for barium-free samples, from energy splitting of the Mn3s-spectra components. Strong heterogeneousness of the crystals both in elemental composition and crystal structure is discovered. It is shown that the heterogeneousness displays itself in various oxygenic environments around Mn atoms which give rise to the appearance of Mn4+ ions. A simple model is proposed that allows understanding the nature of the appearance of Mn4+ ions in single crystals of lanthanum–bismuth manganites.