S. Sato

Bio: S. Sato is an academic researcher from Yamagata University. The author has contributed to research in topics: Magnetic field & Thin film. The author has an hindex of 4, co-authored 5 publications receiving 33 citations.

Microwave surface resistance of YBCO superconducting thin films under high DC magnetic field

Abstract: We investigated the dc magnetic field and temperature dependences of the microwave surface resistance ( R s ) of YBa 2 Cu 3 O y (YBCO) superconducting thin films with various thicknesses. We used YBCO thin films with 300, 500, and 700 nm deposited on a MgO (1 0 0) substrate by the thermal co-evaporation method. The R s was measured using the dielectric resonator method at 21.8 GHz, and a high dc magnetic field of up to 12 T was applied parallel to the c -axis of the YBCO thin films during R s measurements. The R s value of YBCO thin films increased when dc magnetic field was applied. These relationships could be explained by using the two-fluid model for high frequency and low magnetic field limits. We defined the viscous drag coefficient η under the low magnetic limit and the high magnetic field limit as the η low ( B , T , d ) and η high ( B , T , d ), respectively. The η low values were approximately two orders of magnitude greater than η high values. Also, all η low and η high value decreased or saturated as the temperature and film thickness increased. These results show that η under the low and high magnetic field limit depended on the temperature and film thickness.

Introducing Artificial Pinning Centers Into YBCO Thin Films to Improve Surface Resistance in a DC Magnetic Field

Abstract: We investigated the effect of introducing artificial pinning centers (APCs) into YBa2Cu3O7-δ (YBCO) thin films to reduce the microwave surface resistance (Rs) in a high dc magnetic field for high-performance microwave devices with high-quality factor (Q). YBCO thin films with and without APCs were deposited on MgO(100) substrates by using the pulsed laser deposition technique. We used commercial 0, 1.5, 3.0 wt% BaMO3 (BMO, M = Zr, Hf) doped YBCO targets. The δω and δφ of the YBCO thin films increased as BMO doping increased, and the rate of increase appeared to be smaller for BHO doping than for BZO doping. The Rs of these thin films was measured at 21.8 GHz with the dielectric resonator method and a dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the YBCO thin films during the Rs measurements. The Rs of the BMO doped films in the magnetic field was smaller than that of the pure YBCO films. In particular the Rs of the 1.5 wt% BHO doped films was the smallest among all of the films, about half compared with that of the Rs of the pure YBCO films at 4 T and 20 K. As a result, we found that introducing APCs into YBCO thin films is effective for decreasing Rs under a dc magnetic field.

Dependences of microwave surface resistance of HTS thin films on applied dc magnetic fields parallel and normal to the substrate

Abstract: We investigated the dc magnetic field and temperature dependences of microwave surface resistance (Rs) of high-temperature superconductor (HTS) films Previously, we reported that the surface resistance RsRs(n) under a dc magnetic field applied normaly to the substrate increased when increasing the applied magnetic field For NMR application, we have to examine the Rs(p) under the dc magnetic field parallel to the substrate We measured the Rs(p) of the YBCO and DyBCO thin films with a thickness of 500 nm deposited on a MgO (100) substrate using the dielectric resonator method at 218 GHz, and a dc magnetic field of up to 5 T In a zero magnetic field, the values of Rs(n) and Rs(p) were 035 mQ at 20 K Under the dc magnetic field, the Rs(n) and the Rs(p) also increased with increasing magnetic field, however, the Rs(p) had a lower magnetic field dependence and the value was about 1/10 of that of the Rs(n) The Rs(p) at 164 T and at 700 MHz could be estimated by the two-fluid model The Rs(p) value was about 1/2600 compared with that of copper at 20 K As a result, we clarified that 500 nm thick YBCO and DyBCO thin films could provide advantages for NMR application

Experimental study in the development of HTS NMR probe

Abstract: We investigated the effect of introducing artificial pinning centers (APCs) into YBa2Cu3O7-δ (YBCO) thin films to improve the critical current density (Jc) and reduce the microwave surface resistance (Rs) in a high dc magnetic field. Introduction of the APC was realized by dispersing BaHfO3(BHO) particulates in the YBCO thin films. Four types of sintered YBCO ceramics with x wt % (x = 0.5, 1.0, 2.0) BHO were used as laser targets in order to fabricate YBCO thin films with various amounts of BHO and investigate the influence of the BHO doping concentration. Jc was measured by a four probe method. We measured Jc in a magnetic field which was applied parallel to the c-axis (Jc(p)), and Jc in a magnetic field which was applied perpendicular to the c-axis (Jc(n)). The Rs was calculated using a correlating equation of Jc and Rs. The Jc(p) at 5 T and 20 K of 1.5 wt% BHO doped YBCO thin film was the largest at 3.4 MA/cm 2 . The Jc(n) of 1.5 wt% BHO doped YBCO thin film was 2.5 MA/cm 2 , which is comparable to non-doped. The Rs(n) and Rs(p) of all YBCO thin films was less than 25 μΩ at 500 MHz. Therefore, we clarified the possibility that the most effective way to fabricate thin film for NMR coil application is by doping YBCO with BHO 1.5 wt%.

YBa2Cu3O7 microwave resonators for strong collective coupling with spin ensembles

Abstract: Coplanar microwave resonators made of 330 nm-thick superconducting YBa2Cu3O7 have been realized and characterized in a wide temperature (T, 2–100 K) and magnetic field (B, 0–7 T) range. The quality factor (QL) exceeds 104 below 55 K and it slightly decreases for increasing fields, remaining 90% of QL(B=0) for B = 7 T and T = 2 K. These features allow the coherent coupling of resonant photons with a spin ensemble at finite temperature and magnetic field. To demonstrate this, collective strong coupling was achieved by using di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium organic radical placed at the magnetic antinode of the fundamental mode: the in-plane magnetic field is used to tune the spin frequency gap splitting across the single-mode cavity resonance at 7.75 GHz, where clear anticrossings are observed with a splitting as large as ∼82 MHz at T = 2 K. The spin-cavity collective coupling rate is shown to scale as the square root of the number of active spins in the ensemble.

YBCO microwave resonators for strong collective coupling with spin ensembles

Abstract: Coplanar microwave resonators made of 330 nm-thick superconducting YBCO have been realized and characterized in a wide temperature ($T$, 2-100 K) and magnetic field ($B$, 0-7 T) range. The quality factor $Q_L$ exceeds 10$^4$ below 55 K and it slightly decreases for increasing fields, remaining 90$\%$ of $Q_L(B=0)$ for $B=7$ T and $T=2$ K. These features allow the coherent coupling of resonant photons with a spin ensemble at finite temperature and magnetic field. To demonstrate this, collective strong coupling was achieved by using DPPH organic radical placed at the magnetic antinode of the fundamental mode: the in-plane magnetic field is used to tune the spin frequency gap splitting across the single-mode cavity resonance at 7.75 GHz, where clear anticrossings are observed with a splitting as large as $\sim 82$ MHz at $T=2$ K. The spin-cavity collective coupling rate is shown to scale as the square root of the number of active spins in the ensemble.

Microscopic adaptation of BaHfO3 and Y2O3 artificial pinning centers for strong and isotropic pinning landscape in YBa2Cu3O7–x thin films

Abstract: A study of 3 vol% Y2O3 + 2–6 vol% BaHfO3 double-doped YBa2Cu3O7–x (BHO DD) epitaxial thin films was carried out to explore the morphology adaption of c-axis aligned one-dimensional BHO artificial pinning centers (1D APCs) to secondary Y2O3 nanoparticles (3D APCs). BHO 1D APCs have been predicted to have the least rigidity in an elastic strain energy model in APC/YBa2Cu3O7–x nanocomposite films. Consequently, they could be best 'tuned' away from the c-axis alignment by local strains generated by the Y2O3 3D APCs. This provides an opportunity to generate mixed-morphology APCs, especially at high BHO concentrations. Motivated by this, we have carried out a systematic study of the transport critical current density J c(H, T, θ) on the BHO DD samples in magnetic fields (H) up to 90 kOe at different H orientations from H//c-axis (θ = 0), to θ = 45°, and to H//ab-plane (θ = 90°). Enhanced pinning at all three orientations was observed as illustrated in the comparable low alpha (α) values in the range of 0.13–0.25 at 65 K, which is consistent with the mixed 1D (in c-axis) + 2D (in ab-plane) + 3D APCs observed in transmission electron microscopy (TEM). Upon increasing BHO concentration from 2 to 4 vol%, a monotonic increase of the accommodation field H* at θ = 0°, 45° and 90° was observed, indicative of the APC concentration increase of the mixed morphologies. At 6 vol% BHO, the H* continues the increase to 85 kOe at H//c-axis (θ = 0), and >90 kOe H//ab-plane (θ = 90°), while it decreases from 80 to 85 kOe at 2–4 vol% to 60 kOe at 6 vol% at θ = 45°, which is consistent with the TEM observation of the connection of 3D APCs, appeared at lower BHO concentration into 2D ones in ab-plane at the higher BHO concentrations. These results shed light on the quantitative adaptation of APCs of mixed morphologies with increasing BHO doping in the BHO DD thin films and are important for controlling the APC pinning landscape towards minimal angular dependence.