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The addition of artificial pinning centers has led to an impressive increase in critical current density ($J_{\rm c}$) in a superconductor, enabling record-breaking all-superconducting magnets and other applications. $J_{\rm c}$ has reached $\sim 0.2$-$0.3$ $J_{\rm d}$, where $J_{\rm d}$ is the depairing current density, and the numerical factor depends on the pinning optimization. By modifying $\lambda$ and/or $\xi$, the penetration depth and coherence length, respectively, we can increase $J_{\rm d}$. For (Y$_{0.77}$Gd$_{0.23}$)Ba$_2$Cu$_3$O$_y$ ((Y,Gd)123) we achieve this by controlling the carrier density, which is related to $\lambda$ and $\xi$. We also tune $\lambda$ and $\xi$ by controlling the chemical pressure in the Fe-based superconductors, BaFe$_2$(As$_{1-x}$P$_x$)$_2$ films. The variation of $\lambda$ and $\xi$ leads to an intrinsic improvement of $J_{\rm c}$, via $J_{\rm d}$, obtaining extremely high values of $J_{\rm c}$ of $130$ MA/cm$^2$ and $8.0$ MA/cm$^2$ at $4.2$ K, consistent with an enhancement of $J_{\rm d}$ of a factor of $2$ for both incoherent nanoparticle-doped (Y,Gd)123 coated conductors (CCs) and BaFe$_2$(As$_{1-x}$P$_x$)$_2$ films, showing that this new material design is useful to achieving high critical current densities for a wide array of superconductors. The remarkably high vortex-pinning force in combination with this thermodynamic and pinning optimization route for the (Y,Gd)123 CCs reached $\sim 3.17$ TN/m$^3$ at $4.2$ K and 18 T (${\bf H}\parallel c$), the highest values ever reported in any superconductor., Comment: 35 pages, 7 figures

Elastic constants are of great significance, because they are fundamental thermodynamic susceptibilities that connect directly to thermodynamics and electronic structure, as well as to mechanical properties. Resonant ultrasound spectroscopy (RUS) measures non-destructively all fundamental elastic properties by determining the natural frequencies at which a 3D object resonates when is mechanically excited (normal modes). By using an inversion scheme, it is possible to extract the entire elastic tensor of a material with extreme sensitivity in a single frequency sweep using only one, small sample. This makes RUS particularly advantageous to study physical properties of low-symmetry single crystals and textured bulk materials. I will present recent RUS measurement examples of its applications to thermodynamic and materials science problems. I will focus on the effect of texture in elastic constants as a result of mechanical or growth processes and the robustness of results obtained by RUS. In materials such as aluminum that is often considered isotropic but shows clear anisotropy when it is extruded, or 3D printed. Similar but much larger effect is found in additive manufactured stainless steel where the growth process leads to a large anisotropy with a softening of 40%–50% along the build direction.

Elastic constants are thermodynamic susceptibilities, which provide symmetry-resolved insight into phase transitions and material anisotropy. Therefore, their importance spans basic to applied science and engineering. Resonant ultrasound spectroscopy (RUS) is a powerful method to determine elastic constants, because RUS simultaneously measures all elastic constants in small, low symmetry samples with high precision and accuracy. Conventionally, elastic constants in RUS are obtained from resonant frequencies assuming the sample freely resonates. However, achieving free resonance is often incompatible with experimental situations, because such configurations are inherently unstable. This limitation has hindered utilizing RUS to study phases arising in extreme environments like strong magnetic fields. To overcome these obstacles, we introduce a variation of RUS in which small, finite-area contact is maintained between the sample and ultrasonic transducers using an adhesive. First, we establish the conditions under which this clamped point contact can be treated as a small perturbation to free resonance. After comparing predictions from this modelling with experiment, we then experimentally demonstrate the ability to extract elastic constants, and their temperature dependence, with comparable accuracy and precision to conventional RUS. Finally, we show we can reproducibly map phase boundaries in temperature and magnetic fields using our new approach.

Magnetoelastic dilatometry of the piezomagnetic antiferromagnet UO(2) was performed via the fiber Bragg grating method in magnetic fields up to 150 T generated by a single-turn coil setup. We show that in microsecond timescales, pulsed-magnetic fields excite mechanical resonances at temperatures ranging from 10 to 300 K, in the paramagnetic as well as within the robust antiferromagnetic state of the material. These resonances, which are barely attenuated within the 100-µs observation window, are attributed to the strong magnetoelastic coupling in UO(2) combined with the high crystalline quality of the single crystal samples. They compare well with mechanical resonances obtained by a resonant ultrasound technique and superimpose on the known nonmonotonic magnetostriction background. A clear phase shift of π in the lattice oscillations is observed in the antiferromagnetic state when the magnetic field overcomes the piezomagnetic switch field H [Formula: see text] T. We present a theoretical argument that explains this unexpected behavior as a result of the reversal of the antiferromagnetic order parameter at H [Formula: see text].

Magnetoelastic measurements in the piezomagnetic antiferromagnet UO$_{2}$ were performed via the fiber Bragg grating method in magnetic fields up to $150\,\mathrm{T}$ generated by a single-turn coil setup. We show that in short timescales, order of a few micro seconds, pulsed-magnetic fields excite mechanical resonances at temperatures ranging from $10\,\mathrm{K}$ to $300\,\mathrm{K}$, in the paramagnetic as well as within the robust antiferromagnetic state of the material. These resonances, which are barely attenuated within the 100 ms observations, are attributed to the strong magnetoelastic coupling in UO$_{2}$ combined with the high crystallographic quality of the single crystal samples. They compare well with mechanical resonances obtained by a resonant ultrasound technique and superimpose on the known non-monotonic magnetostriction background. A clear phase-shift of $\pi$ in the lattice oscillations is, unexpectedly, observed in the antiferromagnetic state when the magnetic field overcomes the piezomagnetic switch-field $H_c \simeq -18\,\mathrm{T}$. We further present simulations and a theoretical argument to explain the observed phenomena., Comment: 9 pages, 5 figures

Magnetic skyrmions are well-suited for encoding information because they are nano-sized, topologically stable, and only require ultra-low critical current densities $j_c$ to depin from the underlying atomic lattice. Above $j_c$ skyrmions exhibit well-controlled motion, making them prime candidates for race-track memories. In thin films thermally-activated creep motion of isolated skyrmions was observed below $j_c$ as predicted by theory. Uncontrolled skyrmion motion is detrimental for race-track memories and is not fully understood. Notably, the creep of skyrmion lattices in bulk materials remains to be explored. Here we show using resonant ultrasound spectroscopy--a probe highly sensitive to the coupling between skyrmion and atomic lattices--that in the prototypical skyrmion lattice material MnSi depinning occurs at $j_c^*$ that is only 4 percent of $j_c$. Our experiments are in excellent agreement with Anderson-Kim theory for creep and allow us to reveal a new dynamic regime at ultra-low current densities characterized by thermally-activated skyrmion-lattice-creep with important consequences for applications., 28 pages, 4+4 figures, 1 table. arXiv admin note: substantial text overlap with arXiv:1711.08873

The past years have witnessed major advancements in all-electrical doping control on cuprates. In the vast majority of cases, the tuning of charge carrier density has been achieved

The past years have witnessed major advancements in all-electrical doping control on cuprates. In the vast majority of cases, the tuning of charge carrier density has been achieved via electric field effect by means of either a ferroelectric polarization or using a dielectric or electrolyte gating. Unfortunately, these approaches are constrained to rather thin superconducting layers and require large electric fields in order to ensure sizable carrier modulations. In this work, we focus on the investigation of oxygen doping in an extended region through current-stimulated oxygen migration in YBa2Cu3O7−δ superconducting bridges. The underlying methodology is rather simple and avoids sophisticated nanofabrication process steps and complex electronics. A patterned multiterminal transport bridge configuration allows us to electrically assess the directional counterflow of oxygen atoms and vacancies. Importantly, the emerging propagating front of current-dependent doping δ is probed in situ by optical microscopy and scanning electron microscopy. The resulting imaging techniques, together with photoinduced conductivity and Raman scattering investigations, reveal an inhomogeneous oxygen vacancy distribution with a controllable propagation speed permitting us to estimate the oxygen diffusivity. These findings provide direct evidence that the microscopic mechanism at play in electrical doping of cuprates involves diffusion of oxygen atoms with the applied current. The resulting fine control of the oxygen content would permit a systematic study of complex phase diagrams and the design of electrically addressable devices., The authors acknowledge the financial support from the Fonds de la Recherche ScientifiqueFNRS, Spanish Ministry of Economy and Competitiveness through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015- 0496), SUMATE project (RTI2018-095853-B-C21), cofinanced by the European Regional Development Fund, the COST programme NanoCoHybri (CA 16218), and from the Catalan Government with 2017 SGR 1519. The work of A. Fernańdez-Rodriǵuez has been done in the framework of the doctorate in Materials Science of the Autonomous University of Barcelona (UAB) and is supported by the Spanish Ministry of Economy (BES-2016-077310). The work of A. V. Silhanek is partially supported by the grant CDR J.0151.19 of the F.R.S.- FNRS. S. Blanco Alvarez, S. Melinte, and A. V. Silhanek acknowledge financial support through the grant PDR T.0106.16 of the F.R.S.-FNRS. S. Marinković acknowledges support from F.R.S.-FNRS (Research Fellowship ASP). B. Maiorov was supported by the U.S. DOE, Office of Science, BES, Materials Sciences and Engineering Division. The authors thank the ULiege Microscopy facility CAREM for the SEM investigations. G. Rius acknowledges the Ramon y Cajal grant RYC-2016-21412.

Resonant Ultrasound Spectroscopy (RUS) is an ultrasound-based minimal-effort high-accuracy elastic modulus measurement technique. RUS as described here uses the mechanical resonances (normal modes of vibration or just modes) of rectangular parallelepiped or cylindrical specimens with a dimension of from a fraction of a millimeter to as large as will fit into the apparatus. Provided here is all that is needed so that the reader can construct and use a state-of-the-art RUS system. Included are links to open-source circuit diagrams, links to download Los Alamos National Laboratory open-source data acquisition software, links to request free analysis software, procedures for acquiring measurements, considerations on building transducers, 3-D printed stage designs, and a full mathematical explanation of how the analysis software extracts elastic moduli from resonances.

We describe construction of a new multiphase equation of state (EOS) for beryllium calibrated almost entirely to density functional theory calculations based on the AM05 exchange-correlation functional. The EOS is in tabular form (as SESAME 92025) and includes hcp, bcc, and liquid/plasma phases. We find hcp→bcc transitions at ∼325 GPa at zero and room temperatures, and at ∼150 GPa on the Hugoniot. Shock melting from the bcc phase proceeds at 205-230 GPa. We also present experimental results for the isentropic bulk modulus as a function of temperature, based on resonant ultrasound spectroscopy measurements.

Magnetic skyrmions are stable nanosized spin structures that can be displaced at low electrical current densities. Because of these properties, they have been proposed as building blocks of future electronic devices with unprecedentedly high information density and low energy consumption. The electrical detection of an ordered skyrmion lattice via the Topological Hall Effect (THE) in a bulk crystal, has so far been demonstrated only at cryogenic temperatures in the MnSi family of compounds. Here, we report the observation of a skyrmion lattice Topological Hall Effect near room temperature (276 K) in a mesoscopic lamella carved from a bulk crystal of FeGe. This region coincides with the skyrmion lattice location revealed by neutron scattering. We provide clear evidence of a re-entrant helicoid magnetic phase adjacent to the skyrmion phase, and discuss the large THE amplitude (5 nΩ.cm) in view of the ordinary Hall Effect.

The elastic properties of U3Si2 at room temperature have been measured via resonant ultrasound spectroscopy. Results show that the average value of Young's and the bulk modulus for U3Si2 are 130.4 ± 0.5 and 68.3 ± 0.5 GPa, respectively. Further, a numerical model to assess thermal stress in an operating fuel is evaluated. The thermal stress evolved in U3Si2 is compared to UO2 to facilitate an estimation of the probability of crack formation in U3Si2 under representative light water reactor operating conditions.

The mechanical interaction between the fuel and cladding that occurs during operation of a nuclear reactor is important to understand as it can lead to cladding failures and release of radioactive material into the coolant. In order to develop better models of the pellet-clad mechanical interactions , the mechanical properties of the fuel at relevant operating temperatures, like the elastic moduli, are needed for current and advanced accident tolerant fuels (ATFs). In this work, elevated temperature nanoindentation and resonant ultrasound spectroscopy were used to measure the moduli and hardness of several fluorite materials (CeO2, ThO2, UO2) and several ATF candidates (ATF) (U3Si2, UN, UB2). In addition, a comparison of the two techniques was performed in this study to independently validate the mechanical properties.

We report a detailed study of the magnetization modulus as a function of temperature and applied magnetic field under varying angle in Sr$_{4}$Ru$_{3}$O$_{10}$ close to the metamagnetic transition at $H_{c}\backsimeq 2.5\,$T for $H \perp c$. We confirm that the double-feature at $H_{c}$ is robust without further splitting for temperatures below 1.8 K down to 0.48 K. The metamagnetism in Sr$_{4}$Ru$_{3}$O$_{10}$ is accompanied by a reduction of the magnetic moment in the plane of rotation and large field-hysteretic behavior. The double anomaly shifts to higher fields by rotating the field from $H\,\perp \,c$ to $H\,\parallel\,c$. We compare our experimental findings with numerical simulations based on spin reorientation models caused by intrinsic magnetocrystalline anisotropy and Zeeman effect. Crystal anisotropy is able to explain a metamagnetic transition in the ferromagnetic ordered system Sr$_{4}$Ru$_{3}$O$_{10}$, but a Dzyaloshinskii-Moriya term is crucial to account for a reduction of the magnetic moment as discovered in the experiments., Comment: 7 pages, 8 figures

We present magnetization measurements on Sr 4 Ru 3 O 10 as a function of temperature and magnetic field applied perpendicular to the magnetic easy c-axis inside the ferromagnetic phase. Peculiar metamagnetism evolves in Sr 4 Ru 3 O 10 below the ferromagnetic transition T C as a double step in the magnetization at two critical fields H c 1 and H c 2 . We map the H − T phase diagram with special focus on the temperature range 50 K ≤ T ≤ T C . We find that the critical field H c 1 ( T ) connects the field and temperature axes of the phase diagram, whereas the H c 2 boundary starts at 2.8 T for the lowest temperatures and ends in a critical endpoint at (1 T; 80 K). We conclude from the temperature dependence of the ratio Hc 1 Hc 2 ( T ) that the double metamagnetic transition is an intrinsic effect of the material and it is not caused by sample stacking faults such as twinning or partial in-plane rotation between layers.

A very strong magnetoelastic effect in the ${\mathrm{CeCo}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{Si}$ alloys is reported. The strength of the magnetostrictive effect can be tuned upon changing $x$. The moderate low-temperature linear magnetostriction observed at low Fe concentrations becomes very large $(\frac{\mathrm{\ensuremath{\Delta}}L}{L}\left(16T,2K\right)=\phantom{\rule{4pt}{0ex}}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3})$ around the critical concentration ${x}_{c}\ensuremath{\approx}0.23$ at which the long-range antiferromagnetic order vanishes. Upon increasing doping through the nonmagnetic region $(xg{x}_{c})$, the magnetostriction strength gradually weakens again. The interplay between magnetic order and the Kondo screening appears to cause an enhanced valence susceptibility slightly changing the Ce ions valence, ultimately triggering the large magnetostriction observed around the critical concentration. Previous studies of the evolution of the lattice parameters with $x$ as well as magnetization and x-ray absorption spectroscopy measurements support this hypothesis.

Non-linear electrical transport studies at high-pulsed magnetic fields, above the range accessible by DC magnets, are of direct fundamental relevance to the physics of superconductors, domain-wall, charge-density waves, and topological semi-metal. All-superconducting very-high field magnets also make it technologically relevant to study vortex matter in this regime. However, pulsed magnetic fields reaching 100 T in milliseconds impose technical and fundamental challenges that have prevented the realization of these studies. Here, we present a technique for sub-microsecond, smart, current-voltage measurements, which enables determining the superconducting critical current in pulsed magnetic fields, beyond the reach of any DC magnet. We demonstrate the excellent agreement of this technique with low DC field measurements on Y$_{0.77}$Gd$_{0.23}$Ba$_2$Cu$_3$O$_7$ coated conductors with and without BaHfO$_3$ nanoparticles. Exploring the uncharted high magnetic field region, we discover a characteristic influence of the magnetic field rate of change ($dH/dt$) on the current-voltage curves in a superconductor. We fully capture this unexplored vortex physics through a theoretical model based on the asymmetry of the vortex velocity profile produced by the applied current., Comment: 9 pages, 7 figures

Elastic moduli are fundamental thermodynamic susceptibilities that connect directly to thermodynamics, electronic structure and mechanic properties. Thus, determining the changes of elastic moduli as a function of time and temperature is a powerful tool to study a variety of phenomena. The Resonant Ultrasound Spectroscopy (RUS) technique is based on the measurement of mechanical resonance frequencies that can be made with extreme precision and used to compute the elastic moduli without corrections. In this talk, I will give show several examples of the use of RUS in different systems, ranging from magnetic phase transition, determining very small degrees of elastic anisotropy in metals as well as changes in time product of radioactive decay. I will discuss the latest advances made at Los Alamos on measuring and determination of elastic constants. This allow to track the resonance position with high precision, obtaining moduli with an absolute precision of 0.5% and relative changes smaller than part per 10 million.

In a recent PNAS paper (1) we explain the anomalous temperature dependence of the elasticity in δ-plutonium (δ-Pu) in terms of a first-principles model that includes multiple energy configurations attributed to spin fluctuations. Our model (1) captures the highly unusual behavior of decreasing elastic moduli with increasing temperature at constant volume. This is a falsifiable test that any model must pass but none, other than the one we present (1), has. This test is a difficult one, as usually the smaller volume state required to keep volume constant is elastically stiffer, contrary to measurements. Our theory yields a modest decrease by about … [↵][1]1To whom correspondence should be addressed. Email: migliori{at}lanl.gov. [1]: #xref-corresp-1-1

We investigate the anisotropic nature of magnetocrystalline coupling between the crystallographic and skyrmion crystal (SKX) lattices in the chiral magnet MnSi by magnetic field-angle resolved resonant ultrasound spectroscopy. Abrupt changes are observed in the elastic moduli and attenuation when the magnetic field is parallel to the [011] crystallographic direction. These observations are interpreted in a phenomenological Ginzburg-Landau theory that identifies switching of the SKX orientation to be the result of an anisotropic magnetocrystalline coupling potential. Our paper sheds new light on the nature of magnetocrystalline coupling potential relevant to future spintronic applications., Comment: 6+4 pages, 5+3 figures

Superconductors are excellent testbeds for studying vortices, topological excitations that also appear in superfluids, liquid crystals, and Bose-Einstein condensates. Vortex motion can be disruptive; it can cause phase transitions, glitches in pulsars, and losses in superconducting microwave circuits, and it limits the current carrying capacity of superconductors. Understanding vortex dynamics is therefore of fundamental and technological importance, and the competition between the effects of thermal energy and energy barriers defined by material disorder is not completely understood. In particular, early measurements of thermally-activated vortex motion (creep) in iron-based superconductors unveiled fast rates (S) comparable to measurements of YBa2Cu3O7 (YBCO). This was puzzling because S is thought to somehow positively correlate with the Ginzburg number (Gi), and Gi is orders of magnitude lower in most iron-based superconductors than in YBCO. Here, we report very slow creep in BaFe2(As0.67P0.33)2 films, and propose that there is a universal minimum realizable (where Tc is the superconducting transition temperature) that has been achieved in our films, few other materials, and violated by none. This limitation provides new clues on how to design materials with slow creep and helps elucidate open questions regarding the interplay between system-specific length scales and vortex dynamics.

We show a simple and effective way to improve the vortex irreversibility line up to very high magnetic fields (60T) by increasing the density of second phase BaZrO3 nanoparticles. (Y0.77,Gd0.23)Ba2Cu3Oy films were grown on metal substrates with different concentration of BaZrO3 nanoparticles by the metal organic deposition method. We find that upon increase of the BaZrO3 concentration, the nanoparticle size remains constant but the twin-boundary density increases. Up to the highest nanoparticle concentration (n ~ 1.3 × 1022/m3), the irreversibility field (Hirr) continues to increase with no sign of saturation up to 60 T, although the vortices vastly outnumber pinning centers. We find extremely high Hirr, namely Hirr = 30 T (H||45°) and 24 T (H||c) at 65 K and 58 T (H||45°) and 45 T (H||c) at 50K. The difference in pinning landscape shifts the vortex solid-liquid transition upwards, increasing the vortex region useful for power applications, while keeping the upper critical field, critical temperature and electronic mass anisotropy unchanged.

Second-generation (2G) HTS wires are now being produced routinely in kilometer lengths using Metal Organic Chemical Vapor Deposition (MOCVD) process with critical currents of 300 A/cm. While this achievement is enabling several prototype devices, in order to reach a substantial commercial market, the cost-performance metrics of 2G HTS wires need to be significantly improved in device operating conditions. Zr-doping has been found to be an effective approach to improve in-field critical current performance of MOCVD-based HTS wires. In this work, we have explored modifications to the Zr-doped precursor compositions to achieve three and two-fold increase in deposition rate in research and production MOCVD systems respectively. Production wires made with modified Zr-doped compositions exhibit a self-field critical current density of 50 MA/cm2 at 4.2 K and a 55 to 65% higher performance than our previous wires with Zr-doping, over magnetic field range of 0 to 30 T. We have also developed an alternate, low-cost technique, namely electrodeposition, to deposit silver overlayer on superconducting film. Wires made with electrodeposited silver are able to sustain the same level of overcurrent as sputtered silver layers. This process has been successfully scaled up to 100 m lengths.

Numerous experimental results have suggested that the J c of YBa 2 Cu 3 O 7 (YBCO) films is significantly higher near the film–substrate interface than in the remainder of the film. We previously proposed that this effect is due to interfacial pinning enhancement caused by stress and the resulting misfit dislocations at the heteroepitaxial interface. To test this hypothesis we have used a non-superconducting PrBa 2 Cu 3 O 7− δ (PrBCO) buffer layer to minimize the lattice mismatch with YBCO. We find that the PrBCO layers lower J c of the 0.4 μm YBCO films in a predictable way, and that, if sufficiently thick (∼0.5 μm), they eliminate interfacial enhancement altogether. Our interpretation of this result is that the defects responsible for interfacial enhancement of flux pinning originate at the bottom of the non-superconducting PrBCO layer, which screens the pinning centers from vortices in YBCO. This result demonstrates that the pinning enhancement arises from stress at the film–substrate interface.

In this work we describe the effects of adding different amount of single-wall (sw) carbon nanotubes (CNT) on the superconducting properties of MgB 2. We observed that the amount of swCNT that partially dilute into the MgB 2 matrix is lower than for double-wall (dw) CNT samples for the same nominal content. This C incorporation leads to an increase of the upper critical field (Hc2), with a maximum Hc2(0) extrapolated value of 33.5 T, expected for a two-gap superconductor in the dirty limit. At the same time, the fraction of swCNT that has not been incorporated into MgB 2 lattice may retain their structural integrity acting as strong vortex pinning centers. In this case the optimum nominal swCNT content for increasing critical current density (Jc) is in the range 7.5-10%at.

A composite layer has been successfully implemented in high temperature superconducting (HTS) coated conductors (CCs) based on ion beam assisted deposition (IBAD) MgO technology. This layer serves a dual function: a nucleation layer for the growth of high quality biaxially aligned MgO and a diffusion barrier to inhibit interdiffusion between the Ni-alloy substrate and the superconductor. The composition of the composite Y2O3-Al2O3 influences the texture and superconducting properties of YBCO films grown on STO buffered MgO/Y2O3-Al2O3/Ni-alloy. Our experimental results demonstrate that the superconducting properties of YBCO grown on STO buffered MgO/Y2O3-Al2O3/Ni-alloy are comparable with those of YBCO on standard architecture. The use of a single composite Y2O3-Al2O3 layer instead of individual layers of Y2O3 and Al2O3 for the fabrication of HTS CCs based on IBAD MgO provides advantages such as simplified architecture and potentially reduced cost due to the reduced number of fabrication steps.

YBa2Cu3O7-x (YBCO) thick films were grown by hybrid liquid phase epitaxy (HLPE) on (001) SrTiO3 (STO) substrates. With introduction of Au into the film via diffusion from a 5 mol.% 100 nm thick Au-doped STO buffer, self-field Jcs at 77 K of ~ 2.4 MAcm-2 and I cs up to 700 A/cm-width of were achieved. The J c value is virtually independent on thickness and growth rates are extremely high ( ~ 1 mum/min) without the need for post-growth processing. From transmission electron microscopy (TEM), Y2O3 nano-cloud extended defects ( ~ 100 nm size), but < 100 nm apart, were identified as the pinning defects in the films. The single crystal results were successfully translated to tapes, giving self-field Ics of around 300 A/cm-width.

Retaining a dissipation-free state while carrying large electrical currents is a challenge that needs to be solved to enable commercial applications of high-temperature superconductivity. Here, we show that the controlled combination of two effective pinning centres (randomly distributed nanoparticles and self-assembled columnar defects) is possible and effective. By simply changing the temperature or growth rate during pulsed-laser deposition of BaZrO(3)-doped YBa(2)Cu(3)O(7) films, we can vary the ratio of these defects, tuning the field and angular critical-current (Ic) performance to maximize Ic. We show that the defects' microstructure is governed by the growth kinetics and that the best results are obtained with a mixture of splayed columnar defects and random nanoparticles. The very high Ic arises from a complex vortex pinning landscape where columnar defects provide large pinning energy, while splay and nanoparticles inhibit flux creep. This knowledge is used to produce thick films with remarkable Ic(H) and nearly isotropic angle dependence.

To understand the origin of the increase in critical current density of rare earth barium cuprate superconductor thin films with decreasing thickness, a series of sub-300-nm EuBa 2 Cu 3 O 7-δ thin films deposited on SrTiO 3 substrates are studied by X-ray diffraction and electrical transport measurements. The out-of-plane crystallographic mosaic tilt and the out-of-plane microstrain both increase with decreasing film thickness. The calculated density of c-axis threading dislocations matches the extent of the observed low-field enhancement in critical current density for fields applied parallel to c. The inplane mosaic twist and in-plane microstrain are both around twice the magnitude of the out-of-plane values, and both increase with decreasing film thickness. The results are consistent with the observed stronger field enhancement in critical current density for fields applied parallel to ab. The lattice parameter variation with thickness is not as expected from consideration of the biaxial strain with the substrate, indicative of in-plane microstrain accommodation by oxygen disorder. Collectively, the results point to an enhancement of critical current by interfacial strain induced oxygen disorder which is greatest closest to the film-substrate interface. The findings of this study have important implications for other thin functional oxide perovskite films and nanostructures where surface and interfacial strains dominate the properties.

In thin films of rare-earth manganites, RE1−xMxMnO3 (RE=rare earth, M=Ca, Sr, Ba), with mixed-valence perovskite structure, the transport properties highly depend on the deposition technique, processing conditions, and the substrate used. Chemical solution deposition techniques provide many advantages, such as low cost, easy setup, and coating of large areas. However, the crystalline quality, uniformity, and reproducibility of the film depend on the reactivity of the chemical used for solution preparation. In this paper, we report a novel process to grow rare-earth manganite films using low-cost polymer-assisted deposition technique. In this process, polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and a uniform film. These solutions were stable, and crack-free films were obtained using these solutions. In this paper, thin films of La1−xSrxMnO3, La1−xCaxMnO3, and Pr0.5Ca0.5MnO3 were grown on (001) LaAlO3 substrates. The La1−xSrxMnO3 and La1−xCaxMnO3 films were highly c-axis oriented and epitaxial, and showed high magnetoresistance near their Curie temperature. Charge ordering was observed in the Pr0.5Ca0.5MnO3 film at 220 K and high magnetoresistance of nearly −100% was obtained at low temperatures. The structural, transport, and magnetic properties of these films were similar to those obtained for films grown by physical vapor deposition.

High critical current densities (J{sub c}) in thick films of the Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO, {Tc}{approx}92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application-dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect-free conductor in which the grain-to-grain connectivity maintains levels of inter-grain J{sub c} that are comparable to the intra-grain J{sub c}. That is, high critical current (I{sub c}) YBCO coated conductors must contain engineered in homogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high-performance YBCO coated-conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano-engineer the microstructure for tunable superconducting wires. Multi-scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher I{sub c} wires for large-scale, commercial applicationmore » are discussed within the context of these recent advances.« less

Twenty years ago in a series of amazing discoveries it was found that a large family of ceramic cuprate materials exhibited superconductivity at temperatures above, and in some cases well above, that of liquid nitrogen. Imaginations were energized by the thought of applications for zero-resistance conductors cooled with an inexpensive and readily available cryogen. Early optimism, however, was soon tempered by the hard realities of these new materials: brittle ceramics are not easily formed into long flexible conductors; high current levels require near-perfect crystallinity; and — the downside of high transition temperature — performance drops rapidly in a magnetic field. Despite these formidable obstacles, thousands of kilometres of high-temperature superconducting wire have now been manufactured for demonstrations of transmission cables, motors and other electrical power components. The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost. The remaining task for materials scientists is to return to the fundamentals and squeeze as much performance as possible from these wonderful and difficult materials.

The influence of film thickness and growth rate on the vortex pinning in hybrid liquid phase epitaxy (HLPE) films was explored. Film growth rates as high as 12 nm s−1 (0.7 µm min−1) produced high Jc films. Weak or no thickness dependence was found in films of thickness ranging from 0.4 to 3 µm. Field and angular measurements of the critical current density (Jc) and the power-law exponent (N) of the current–voltage curves were used to determine the nature of pinning. Films thinner than 0.6 µm showed a higher density of correlated defects parallel to the ab plane than thicker films. Using HLPE, it was possible to achieve very strong pinning in films ~3 µm thick, yielding critical currents over 300 A cm−1 width at self-field, and as high as 35 A cm−1 width at μ0H = 3 T at T = 75.5 K. Decreasing the deposition rate allowed improving the high field performance, opening up the possibility to engineer the pinning landscape of the HLPE films.

Biaxially textured SmxZr1-xOy (SZO) thin films have been grown directly on an ion beam assisted deposited (IBAD) MgO template, without using an intermediate homoepitaxial MgO layer. SZO buffer layers were deposited using reactive magnetron sputtering of a Sm (50 at.%)-Zr (50 at.%) alloy target. The SZO texture is similar to that of the MgO template. Epitaxial YBCO films, ~1mum-thick, grown by pulsed laser deposition on SZO buffered coated conductors have high critical current densities. The in-field measurements indicate that superconducting samples with SZO as buffer are as good as STO/homoepitaxial MgO buffered samples. These results demonstrate that SZO is an appropriate buffer for the fabrication of low cost YBCO/IBAD MgO coated conductors with excellent transport properties.

Two different types of defect structures have been identified to be responsible for the enhanced pinning in metal organic deposited YBCO films. Rare earth additions result in the formation of nanodots in the YBCO matrix, which form uncorrelated pinning centers, increasing pinning in all magnetic field orientations. 124-type intergrowths, which form as laminar structures parallel to the ab-plane, are responsible for the large current enhancement when the magnetic field is oriented in the ab-plane. TEM studies showed that the intergrowths emanate from cuprous containing secondary phase particles, whose density is partially controlled by the rare earth doping level. Critical process parameters have been identified to control this phase formation, and therefore, control the f 24 intergrowth formation. This work has shown that through process control and proper conductor design, either by adjusting the composition or by multiple coatings of different functional layers, the desired angular dependence can be achieved.

Key features of the microstructure in high critical current density (JC ) MOD Y1Ba2Cu3Oy (YBCO) films on biaxially-textured nickel substrates with intervening buffer layers are presented. 0.8 mum thick MOD YBCO films on the 4cm wide RABiTS templates have 77K, self-field JC and IC values exceeding 3 MA/cm2 and 250A/cm-width, respectively. MOD YBCO films have a laminar grain structure with a high density of YBa2Cu4Oy(Y124) intergrowths, which give rise to an enhanced peak in angular anisotropy measurements of JC when the applied field is parallel to the ab planes of the YBCO films. Other key aspects of MOD YBCO films related to the laminar growth mode and layered microstructure are grain boundary overgrowth, grain boundary meandering, colony microstructures, incoherent precipitates of Y2O3 and Y2Cu2O5, and phase separations.

The effects of adding Er3+ to the trifluoroacetate precursor solution used to produce YBa2Cu3O7-times thin films by the MOD method have been investigated. Er-added MOD YBCO films, applied to RABiTS-based substrates, were examined by in-field transport, electron microscopy, and Raman spectroscopy. Er additions up to Er/Y= 1.0 have been studied. Consequences to the, chemistry, microstructure, and electro-magnetic performance of fully processed coated conductor samples were determined. As expected, the added Er increases the relative concentration of atoms that tend to occupy the ldquoYrdquo position in the YBCO lattice, however, Er3+ crystal field effects seen in Raman spectra of the Er-added samples indicate that there is little or no Er substitution on the Ba or Cu2 sites. Some Er3+appears on Y sites in the YBCO; the remainder is found as nano-sized (Er,Y)2O3 precipitates. Current transport measurements as a function of field angle show that Jc increases with H//c but decreases with H//ab as the Er/Y ratio increases towards 0.5. The increased H//c flux pinning is attributed to the Er-rich nano-precipitates; the decreased H//ab flux pinning is attributed to a monotonic reduction in the number of planar defects with increasing Er/Y value.

Microstructural evolution with the change in thickness of superconducting YBa2Cu3O7-X films on single-crystal SrTiO3 substrates deposited by pulsed laser deposition was evaluated using different structural characterization tools. A noticeable degradation of crystallinity with the increased film thickness was detected. Nevertheless, a comprehensive relationship between the microstructure and the zero-field current-density can not be established solely based on the degradation of crystallinity.

The hybrid liquid phase epitaxy (HLPE) approach has the potential to be a high rate-low cost process. This deposition process is used to grow epitaxial YBa2Cu3O7 (YBCO) films in the presence of a thin (100 to 500 nm) liquid BaO-CuO flux layer. Despite the presence of the molten flux, YBCO growth is found to be feasible on technical substrates because of the limited dissolution of the buffer layer in the thin flux layer. The high atom mobility at the growing interface under the liquid flux enables high growth rates (demonstrated to be greater than 10 nmldrs-1 in a wide temperature regime and predicted to be up to ~5 nmldrs-1). We report results on HLPE YBCO films grown on (100) strontium titanate and textured technical substrates such as rolling-assisted biaxially textured substrates (RABiTS) and ion-beam-assisted-deposited (IBAD) MgO. High values of the critical temperature above 90 K and critical current ~400 A per cm width for 3 mum thick films on single crystal substrates and promising high values on technical substrates are obtained. Furthermore, there is potential for making thicker films of the same quality since film density is maintained with thickness. Angular-dependent transport critical current as a function of applied field for these films, as well as microstructural measurements by transmission electron microscopy are also reported. The angular and field dependence of critical current density are similar to standard PLD (pulsed laser deposition) films. Although the films are of high epitaxial quality they contain yttria precipitates which are possible sources of flux pinning centers.

When a current is applied perpendicular to the vortex lattice (VL), Lorentz force may cause the VL to drift and flux-flow dissipation is observed. When the current is parallel to the applied magnetic field in a force-free (FF) configuration, a dissipation is also observed but at higher values of applied current. It has been suggested that pinning as well as free surfaces play an important role in the stabilization of the VL in the FF configuration. In thin YBa2Cu3O7 films, FF configurations can be obtained when Hparab with the current flowing parallel to the ab-planes. In this work we study the influence of thickness, growth method and pinning centers on the dissipation mechanism at variable Lorentz force and FF configurations. Comparisons of experiments done at maximum and variable Lorentz force show that there are two pinning regimes when the field is rotated in these configurations; one consistent with only a decrease in the applied force, indicated by the overlap of the power law exponent of the current-voltage curves as the field is rotated toward the ab-planes, and another very close to the ab-planes, where the dissipation characteristics change.

This study shows that biaxially textured SmxZr1−xOy(SZO) with a wide range of compositions (0.06

The critical current densities Jc−w(H) per unit width of the tape were measured at 75 K in applied magnetic fields H on a 3 µm-thick YBa2Cu3O7 film on a metallic substrate fabricated using the BaF2 process. Jc−w(H) was the highest reported for YBa2Cu3O7 conductors with H perpendicular to the tape, and was independent of the angle between H and the tape plane for μ0H≤3 T. The film did not contain artificial flux-pinning centres, implying the existence of a strong isotropic-pinning centre in undoped YBa2Cu3O7 films, thus opening up unexplored avenues for improving performance of coated conductors.

We have studied the influence of naturally grown SrTiO3 particles at the buffer layer surface on the in-field critical current density (Jc) dependence of coated conductors. The presence of the SrTiO3 particles induces the growth of extra-correlated pinning along the c-axis direction in the YBa2Cu3O7 films that thread samples as thick as 5 µm. These correlated pinning centres produce a bigger c-axis peak and effectively reduce the Jc magnetic field (H) decay characterized by a smaller exponent α of the power law decay. This method opens up a new approach for how to increase Jc under an applied magnetic field without the need for an extra process. This study brings new meaning to the so-called optimal deposition conditions, since it will depend on the field and temperature region of the application.

Pinning in YBa2Cu3O7?x (YBCO) films is compared with mixed rare-earth (RE) films. The field dependence of critical current density and pinning force plots at 75.5?K are analysed. The work provides a guideline as to how to optimize pinning by inclusion of both random and correlated defects. In summary, Y mixed with larger RE ions appears to be optimum for effective pinning across a wide field regime as well as permitting growth at temperatures low enough for technological use.

We have grown a -axis oriented EuBa 2 Cu 3 O 7 thin films on SrTiO 3 (001) substrates using a magnetron sputtering technique. In these films the CuO 2 planes are aligned parallel to the substrates. The film microstructure shows microdomains. The microdomains are grains with a 90° rotation of the c -axis. We have done transport measurements in applied magnetic fields up to 16 T. We have found a reduced quasi-2D dimensionality of the vortex glass transition probably resulting of vortex coherence being limited by disorder at domain boundaries. The activation energy for vortex motion in the liquid state displays a 1/H 0.5 field dependence characteristic of strongly anisotropic superconductor.

SuperPower is focused on scaling up second-generation (2-G) high-temperature superconductor (HTS) technology to pilot-scale manufacturing. The emphasis of this program is to develop R&D solutions for scale-up issues in pilot-scale operations to lay the foundation for a framework for large-scale manufacturing. Throughput continues to be increased in all process steps including substrate polishing, buffer and HTS deposition. 2-G HTS conductors have been produced in lengths up to 100 m. Process optimization with valuable information provided by several unique process control and quality-control tools has yielded performances of 6000–7000 A m (77 K, 0 T) in 50–100 m lengths using two HTS fabrication processes: metal organic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD). Major progress has been made towards the development of practical conductor configurations. Modifications to the HTS fabrication process have resulted in enhanced performance in magnetic fields. Industrial slitting and electroplating processes have been successfully adopted to fabricate tapes in width of 4 mm and with copper stabilizer for cable and coil applications. SuperPower’s conductor configuration has yielded excellent mechanical properties and overcurrent carrying capability. Over 60 m of such practical conductors with critical current over 100 A/cm-width have been delivered to Sumitomo Electric Industries, Ltd. for prototype cable construction.