SmBa2Cu3Oy Films Research Articles

Effect on SmBa2Cu3Oy films of lattice strain induced by BaHfO3 nanorods

BaMO3 (BMO, M=Zr, Sn, Hf, etc.) is well known to undergo self-organisation into many nanorods in a REBCO film grown by vapour phase epitaxy. However, REBCO experiences strain resulting from the BMO nanorods and this strain causes the superconducting properties to deteriorate. In this study, we prepared SmBCO films containing 16 vol% BaHfO3 (BHO) using a pulsed laser deposition method. Deposition was accomplished by using a low-temperature growth (LTG) technique to grow the films even at low substrate temperatures. By decreasing the substrate temperature, the number density of the BHO nanorods, which is estimated from the critical current density in magnetic fields and the irreversibility line, increased and their diameter decreased. The lattice strain exerted upon SmBCO and BHO could conveniently be evaluated by conventional X-ray diffraction owing to the substantial BHO content. This evaluation indicated that, as the substrate temperature decreased, the tensile strain exerted upon SmBCO decreased, whereas the compressive strain experienced by BHO increased. These results indicate that the effect of stress exercised by the narrow nanorods on REBCO is small. Our findings suggest LTG to be an effective technique to prepare REBCO films with a high number density of BMO nanorods owing to the small amount of stress induced by these nanorods.

Investigation of the longitudinal magnetic field effect in SmBa2Cu3Oy films with various shaped artificial pinning centers

The longitudinal magnetic field (LMF) state, in which the magnetic field is applied parallel to the applied current direction and ab-plane of SmBa2Cu3Oy (Sm123) films with shaped artificial pinning centers (APCs) of various shapes is investigated. The in-field critical current density (Jc) of pure Sm123 films in the LMF state and films with Y2O3, Sm2BaCuO5, BaHfO3, and a multilayered structure with short BaHfO3 nanorods were measured in the configuration. The measurement revealed that there was significant Jc enhancement only in the multilayered film. From the viewpoint of flux pinning, 3D flux pinning is key to improving in-field Jc in the LMF state. However, the Sm123 films with APCs, such as Y2O3 and Sm2BaCuO5, did not have a larger Jc than the pure Sm123 films in the LMF state. This indicates that the APCs prevent the current flowing along the external magnetic field. Both of the 3D flux pinning and the pure layer in which current can flow without disturbance are important for the Jc enhancement in the LMF state.

Improved Flux Pinning for High-Field Applications in BaHfO3-Doped SmBa2Cu3 Oy-Coated Conductors With High Density of Random Pinning Centers Induced by BaHfO 3 Nanorods

The critical current performance of REBa 2 Cu 3 Oy-coated conductors must be isotropically improved for use in high-field coil-based applications operated at low temperatures less than 50 K. The high and isotropic critical current densities (Jc) with respect to the directions of the magnetic field under these operating conditions were achieved by a 3.8 vol.% BaHfO3 (BHO)-doped SmBa 2 Cu 3 Oy (SmBCO) film on a metallic substrate deposited with low-temperature growth (L-BHO film). In particular, the L-BHO film attained a high flux pinning force density over 1.5 TN/m 3 at a temperature of 4.2 K. From the anisotropic scaling approach based on the effective mass model, a high density of random pinning centers in the L-BHO film plays an important role in achieving the high J c performance at 4.2 K. In order to reveal the reason why the L-BHO film includes high density of random pinning centers, we compared the flux pinning properties and the dominant flux pinning centers between the L-BHO film and the other two samples: a 3.8 vol.% BHO-doped SmBCO film fabricated with relatively high-temperature growth, and a nondoped SmBCO film fabricated with low-temperature growth. From the comparison, it is revealed that the random pinning centers are induced by BHO nanorods.

Surface Diffusion Constants and Supersaturations in SmBCO Films Prepared by Pulsed Laser Deposition Method

REBa 2 Cu 3 Oy (REBCO, RE = rare earth) coated conductors are required for high current carrying capability. Self-organization of Ba-M-O (BMO, M = Zr, Sn, Hf...) is available to improve critical current density (J c ) in magnetic field, and suppression of a-axis grain growth contributes to enhance J c . The former and latter are affected by the surface diffusion of adatoms and supersaturation in the REBCO film growth, respectively. We focused on surface morphologies of SmBa 2 Cu 3 O y (SmBCO) films deposited by the pulsed laser deposition method in this paper, and estimated surface diffusion constant and supersaturation from the surface morphologies. As a result, an activation energy of the surface diffusion was approximately 2.2 eV and the value is somewhat smaller than 2.5 eV for YBCO films. Additionally, we found that a-axis grains appeared when supersaturation (Δμ) became higher than a threshold Δμ . Interestingly, a seed layer consisting of c-axis oriented SmBCO suppressed a -axis grain growth. These findings are useful to improve J c in REBCO coated conductors.

Superconducting properties and microstructures for Ba2SmNbO6 and BaHfO3 co-doped SmBa2Cu3Oy thin films

Recently, we observed that Ba2SmNbO6 (BSNO), which has a double perovskite structure, forms wide nanorods in a SmBa2Cu3Oy (SmBCO) film when compared with BaHfO3 (BHO) nanorods. These wide nanorods can trap flux quanta effectively in low magnetic fields; on the other hand, narrow nanorods can trap flux quanta in high magnetic fields. In this paper, we doped SmBCO films with BSNO and BHO with the aim of introducing both wide and narrow nanorods and bringing out the flux pinning properties in low and high magnetic fields simultaneously. We investigated their microstructures and superconducting properties, and as a result, we confirmed that wide and narrow nanorods could coexist in the SmBCO films. The wide and narrow nanorods trapped the flux quanta in different magnetic fields. We also explored the optimal composition for BSNO + BHO co-doped SmBCO films. These findings indicate that flux pinning properties can be tuned by the multiple doping of BMO materials.

Flux pinning landscape up to 25 T in SmBa2Cu3Oy films with BaHfO3 nanorods fabricated by low-temperature growth technique

REBa2Cu3Oy superconducting tapes are appropriate for high field magnet applications at low temperatures (i.e. below liquid nitrogen temperature). To clarify the morphology and the volume of the effective pinning center at low temperatures, we used a low-temperature growth technique to fabricate SmBa2Cu3Oy (SmBCO) films with various amounts of BaHfO3 (BHO) nanorods onto MgO-buffered metal substrates produced by ion-beam-assisted deposition; we investigated their flux pinning properties using a 25 T cryogen-free superconducting magnet that was recently developed at Tohoku University. According to the microstructural analysis using transmission electron microscopy, the BHO nanorods have a content-dependent morphology and are aligned for the higher content. The inclined and discontinuous BHO nanorods were observed in SmBCO films with BHO contents up to 3.8 vol%; they show an excellent flux pinning force density (1.5 TN m−3 at 21 T and 4.2 K) even when the magnetic field is perpendicular to the films. Based on the effective mass model for the flux pinning, the random pinning centers are dominant at low temperatures. The correlated flux pinning is stronger for aligned nanorods; however, the random pinning center becomes weaker in the 4.5 vol% BHO-doped films. Therefore, the optimal BHO doping level is approximately 3.8 vol% in terms of the amplitude of the critical current density and the anisotropy from 4.2 K to 20 K because this provides the best mixture of correlated and random flux pinning centers.

Strong flux pinning at 4.2 K in SmBa2Cu3Oy coated conductors with BaHfO3 nanorods controlled by low growth temperature

In order to apply REBa2Cu3Oy (REBCO, RE = rare earth elements or Y) coated conductors in high magnetic field, coil-based applications, the isotropic improvement of their critical current performance with respect to the directions of the magnetic field under these operating conditions is required. Most applications operate at temperatures lower than 50 K and magnetic fields over 2 T. In this study, the improvement of critical current density (Jc) performance for various applied magnetic field directions was achieved by controlling the nanostructure of the BaHfO3 (BHO)-doped SmBa2Cu3Oy (SmBCO) films on metallic substrates. The corresponding minimum Jc value of the films at 40 K under an applied 3 T field was 5.2 MA cm−2, which is over ten times higher than that of a fully optimized Nb–Ti wire at 4.2 K. At 4.2 K, under a 17.5 T field, a flux pinning force density of 1.4 TN m−3 for B//c was realized; this value is among the highest values reported for REBCO films to date. More importantly, the Fp for B//c corresponds to the minimum value for various applied magnetic field directions. We investigated the dominant flux pinning centers of films at 4.2 K using the anisotropic scaling approach based on the effective mass model. The dominant flux pinning centers are random pinning centers at 4.2 K, i.e., a high pinning performance was achieved by the high number density of random pins in the matrix of the BHO-doped SmBCO films.

Peculiar critical current density and irreversibility line in double perovskite Ba2SmNbO6-doped SmBa2Cu3Oy film prepared by Nd:YAG pulsed laser deposition

We prepared SmBa2Cu3Oy (SmBCO) films including Ba2SmNbO6 (BSNO) by Nd:YAG pulsed laser deposition (PLD) on LaAlO3 single-crystalline substrates. The BSNO formed many nanorods with a large diameter of 35 nm, which is the largest nanorod diameter in REBa2Cu3Oy films, and their in-plane distribution was random. The matching field estimated from the number density of 202 µm−2 was 0.42 T. We measured Jc–B curves at various measurement temperatures and these Jc–B curves had a Jc peak at approximately 0.37 T. Interestingly, the irreversibility line showed a “reverse S” shape and an anomalous curve was observed at approximately 0.37 T near Tc. To the best of our knowledge, this is the first time that these distinctive features were found in this sample. We concluded that these peculiar behaviors originated from the large-diameter, straight, and threading BSNO nanorods.

Effect of Nanorod Alignment on Flux Pinning State in BaHfO3 Doped SmBa2Cu3 Oy Films

The effect of the microstructure on the flux pinning state in BaHfO 3 (BHO) nanorods doped SmBa 2 Cu 3 O y (SmBCO) films was investigated using high field magnets with a rotator stage. Films with aligned nanorods showed the strong flux pining along c-axis, which disappears at high magnetic fields. This behavior corresponds to the existence of the Bose glass state in the film, which is also supported by the behaviors of the activation energy and the critical exponent of the liquid-glass transition estimated from the transport properties. Moreover, the field dependencies of the flux pinning force are explained by the flux pinning models for the correlated nanorods and the random pinning centers in the films with the aligned and the firework nanorods structures. The strong relationship is confirmed between the structure of the nanorods and the pinning properties in the BHO doped SmBCO films.

Vortex Pinning Properties at Grain Boundary in SmBa2Cu3 ${\text{O}}_{y}$ Superconducting Films With BaHfO3 Nanorods Controlled via Low-Temperature Growth

We investigated the effect of the BaHfO 3 (BHO) nanorods' configuration on transport properties at artificial grain boundaries (GBs) in SmBa 2 Cu 3 O y (SmBCO) superconducting films. To control the nanorods' configuration at the GBs, we deposited 3.0 vol.% BHO-doped SmBCO films on 5° [001]-tilt bicrystal (LaAlO 3 ) 0.3 (SrAl 0.5 Ta 0.5 O 3 ) 0.7 substrates at relatively low growth temperature of 750 °C via the pulsed laser deposition method adopting a seed layer technique. According to the transport results, the critical current density (J c ) at the GBs was improved in the films with the nanorods at low magnetic fields. In addition, field angular dependence of Jc was also improved for a wide range of field directions with a broad peak for B//c. We estimated that the BHO nanorods in the GBs pinned the Abrikosov-Josephson (AJ) vortices with various directions in the GBs. AJ vortex pinning can be controlled by configuration of a pinning center at GB.

Flux Pinning Properties in BaHfO3-Doped SmBa}2Cu3OyFilms on Metallic Substrates Fabricated With Low Temperature Growth

We have developed SmBa 2 Cu 3 O y (SmBCO) superconducting films with BaHfO 3 (BHO) inclusions on singlecrystalline substrates via a pulsed laser deposition method. We have controlled the morphology of the BHO nanorods within the SmBCO matrix by varying growth temperature during the depositions. In this paper, we fabricated 1.5 vol.% BHO-doped SmBCO films on metallic substrates at 750 °C [low-temperature growth (LTG) film] and 840 °C [high-temperature growth (HTG) film]. The LTG film showed lower flux pinning performance at a relatively high measurement temperature ranging from 65 K to 77 K than the HTG film. However, at a low measurement temperature of 20 K under high magnetic fields, the LTG film exhibited higher flux pinning performance in comparison with the HTG film. The maximum flux pinning force density was more than 520 GN/m 3 at 20 K under 9 T. Even on the metallic substrates, LTG is also helpful in achieving an improved flux pinning performance of SmBCO films at low measurement temperatures under high magnetic fields.

Investigation of the Longitudinal Magnetic Field Effect on Multilayered- Films Fabricated on Single-Crystal and Metal Substrates

We discuss the longitudinal magnetic field (LMF) effect in BaHfO 3 (BHO)-doped multilayered (ML) SmBa 2 Cu 3 Oy (SmBCO) films. We observed critical current density (J c ) enhancement in the form of a J c peak with increasing magnetic fields due to the LMF effect at various measurement temperatures on an ML-SmBCO film fabricated on a single-crystalline substrate. These J c peaks were higher than J c s under self-field, and the J c gain was temperature dependent. We concluded that the J c gain was related to the BHO nanorod diameter and the diameter of flux lines along the ab-plane. We also attempted to determine the J c gain of SmBCO films with a similar film structure that were fabricated on IBAD-MgO-buffered metal substrates.

Vortex pinning at low temperature under high magnetic field in SmBa2Cu3Oy superconducting films with high number density and small size of BaHfO3 nano-rods

We have fabricated 5.6 vol.% BaHfO3 (BHO)-doped SmBa2Cu3Oy (SmBCO) films at a low substrate temperature of 750 °C by using the low temperature growth (LTG) technique with a seed layer. Using the LTG technique, we can obtain a purely c-axis oriented SmBCO film even at low growth temperatures. The LTG technique also greatly increases the number density of BHO nanorods. The size and matching field of the BHO nanorods in the films were 5.4 nm and 9.9 T. Transport measurements were carried out, and a high irreversibility field (Birr) and strong flux pinning force density (Fp) were obtained. The Birr was 15.1 T at 77 K for B//c. The maximum Fp of 407 GN m−3 in 10 T at 40 K and 770 GN m−3 from 9 to 17 T at 20 K have been measured. We believe that the LTG technique can be considered as important for improving of flux pinning performance in BaMO3 (BMO: M = Zr, Sn and Hf)-doped SmBCO coated conductors.

Enhancement of critical current densities by the longitudinal magnetic field effect in multilayered SmBa2Cu3Oy films controlling the film thickness

We report on the film thickness and the interface density dependence of critical current density (Jc) in multilayered SmBa2Cu3Oy (SmBCO) films with short BaHfO3 (BHO) nanorods under the force-free state. In the investigation into the film thickness dependence of Jc, we fixed the layer thickness and changed the total film thickness. However, in the investigation into the interface density dependence of Jc, we fixed the total film thickness and changed each layer’s thickness. We observed the Jc peaks via the longitudinal magnetic field effect on multilayered films which have a certain film thickness of over 400 nm and a certain interface density of over 80 layers/μm. We considered that two types of flux pinning were needed for the Jc enhancement and these were against the force-free torque in the ab plane and the Lorentz force along the c-axis.

Superconducting Properties in SmBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub> Films With High Density of BaHfO<sub>3</sub> Nanorods Fabricated With a Seed Layer

A high density of BaMO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BMO) nanorods within a REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (REBCO) film can be generated by heavy doping of the BMO. This is very effective in improving superconducting properties in high magnetic fields. However, heavy doping causes a significant T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> reduction. Introduction of a high density of BMO nanorods into REBCO films without reduction in T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is required. To this end, we deposited SmBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (SmBCO) films with various amount of BaHfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BHO) by a pulsed laser deposition (PLD) method using a seed-layer technique and a low-temperature growth (LTG) technique. Using this technique, we can fabricate a purely c-axis-oriented SmBCO film even at low substrate temperatures T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . The SmBCO films with BHO were fabricated at low T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> of 750 °C without heavy doping of BHO. As a result, the BHO nanorods became thinner and denser than those within SmBCO films fabricated by conventional PLD methods at high T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . The maximum density was 4780/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">φ</sub> of the film reached 9.9 T. These samples showed high T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (> 90 K). We have therefore successfully fabricated high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> SmBCO films with high densities of BHO nanorods using the LTG technique.

Characteristics of high-performance BaHfO3-doped SmBa2Cu3Oy superconducting films fabricated with a seed layer and low-temperature growth

BaHfO3(BHO)-doped SmBa2Cu3Oy (SmBCO) superconducting films were fabricated with a seed layer and low-temperature growth (LTG technique) via pulsed laser deposition. The LTG technique enables the fabrication of high-quality SmBCO films even at a low substrate temperature during the deposition, and also greatly increases the number density of BHO nano-rods. Transmission electron microscopy observations showed that the 5.6 vol% BHO-doped sample had a high number density [(4.8 ± 0.3) × 103 μm−2] of small (5.4 ± 0.7 nm) BHO nano-rods. This sample exhibits maximum flux pinning forces (Fp) of 405 GN m−3 in 9.0 T at 40 K and 105 GN m−3 in 9.0 T at 65 K. The high density and small size of the nano-rods in a REBa2Cu3Oy matrix (where RE is a rare earth element) is considered to be very effective for enhancing Fp at low temperatures under a high field.

Effect of BaHfO3 introduction on the transport current at the grain boundaries in SmBa2Cu3Oy films

We report the effect of BaHfO3 (BHO) introduction into SmBa2Cu3Oy (SmBCO) films on the transport properties at artificial grain boundaries (AGBs) by comparing pure SmBCO and BHO-doped SmBCO films deposited on bicrystal substrates. Improvement of the critical current density (Jc) at the AGB of BHO-doped SmBCO films was confirmed under the magnetic fields at which Jc was restricted at the AGB. By investigating the superconducting properties and from TEM observations, we found that the in-field Jc value for BHO-doped SmBCO films was improved through flux pinning of the Abrikosov–Josephson vortices by BHO nanorods.

シード層を導入したIBAD-MgO 基板上 BaHfO&lt;sub&gt;3 &lt;/sub&gt;添加SmBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;i&gt;&lt;sub&gt;y &lt;/sub&gt;&lt;/i&gt;薄膜の臨界電流密度向上

The development of rare earth (RE) Ba2Cu3Oy (REBCO) coated conductors has been carried out by many groups. The critical current density (Jc) in high magnetic fields needs to be improved for superconducting applications. We have fabricated BaHfO3 (BHO)-doped SmBa2Cu3Oy films on ion beam-assisted deposition (IBAD)-MgO substrates using pulsed laser deposition (PLD). In this study, we introduce a seed layer technique. As a result, the appropriate growth temperature (Ts) is expanded to higher temperature range without BaCeO3 outgrowth around the interface of the SmBCO and CeO2 cap-layer. We were able to control the configurations of the BHO nanorods within the SmBCO films as compared to the conventional PLD method. The SmBCO + BHO (1.4 vol.%) films, which were fabricated at a Tsupper of 900ºC, showed that the Jc in the magnetic field (B // c) was improved as compared to pure-SmBCO films. Furthermore, the global pinning force density reached 21 GN/m-3 at 77 K in B = 2 T.

Flux Pinning Properties of a SmBa2Cu3O y Film Including High Number Density of BaHfO3 Nano-rods on LaAlO3 Substrate

Flux pinning properties of a BaHfO3 (BHO)-doped SmBa2Cu3Oy (SmBCO) film, which was fabricated by pulsed laser deposition method adopting a seed layer technique, have been investigated. Nano-rods of the film were small in a diameter of 5.4 nm and had high number density (high-n) of 4,775/μm2. The flux pinning properties of the film were compared with a SmBCO film including BHO nano-rods with a larger diameter and a lower number density (low-n). At 65 K, the flux pinning force density of the high-n sample (105.0 GN/m3) showed much higher than that of the low-n sample (70.6 GN/m3).

Flux pinning properties and microstructures of a SmBa2Cu3Oy film with high number density of BaHfO3 nanorods deposited by using low-temperature growth technique

To enhance Jc in high magnetic fields, we fabricated a SmBa2Cu3Oy (SmBCO) film with a high number density (2830/µm2) of BaHfO3 (BHO) nanorods by pulsed laser deposition (PLD) adopting a low-temperature growth (LTG) technique (LTG-SmBCO + BHO). The LTG technique consists of seed layer deposition and subsequent film deposition at a lower temperature. The number density of BHO nanorods in the film was approximately 4 times higher than that in a BHO-doped SmBCO film fabricated by conventional PLD without a seed layer. The flux pinning performance of the LTG-SmBCO + BHO film (Fp = 23.8 GN/m3 at 77 K under 4.5 T) was comparable to the reported record high value of 28.3 GN/m3 at 77 K.