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Masaki Suenaga* and Qiang Li Department of Condensed Matter Physics and Materials Science Brookhaven National Laboratory

ac losses in YBCO films in perpendicular magnetic fields Effects of magnetic substrates. Masaki Suenaga* and Qiang Li Department of Condensed Matter Physics and Materials Science Brookhaven National Laboratory Upton, NY 11973 *Retired.

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Masaki Suenaga* and Qiang Li Department of Condensed Matter Physics and Materials Science Brookhaven National Laboratory

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  1. ac losses in YBCO films in perpendicular magnetic fields Effects of magnetic substrates Masaki Suenaga* and Qiang Li Department of Condensed Matter Physics and Materials Science Brookhaven National Laboratory Upton, NY 11973 *Retired M. Suenaga and Qiang Li, APL 88, 262501 (06) Brookhaven Science Associates U.S. Department of Energy

  2. ac losses in YBCO films in perpendicular magnetic fields Effects of magnetic substrates 1) Review ac losses of thin superconducting films in perpendicular magnetic fields. 2) Illustrate effects of a magnetic Substrate on the ac losses. (M. Suenaga and Qiang Li; APL, 88, 262501). 3) Implication to the transport self-field Jc of superconducting films on a magnetic substrate Brookhaven Science Associates U.S. Department of Energy

  3. H Jc Induced J Bzapplied Bz 0 R J and B in a cylinder in parallel magnetic fields A cylinder/slab J B H R

  4. A disk/strip z H Jc Jc Bz currents Bz applied Bz magn. fields R J c J 0 0 B B a R a R J and B in thin films in perp. magnetic fields A cylinder/slab H

  5. Brookhaven Science Associates U.S. Department of Energy ac losses in YBCO films in perpendicular ac magnetic fields 1) a cylinder: P  (1/JcR)Ba3 for Ba << Bp=2m0JcRP  JcRBa for Ba >> Bp 2) a thin disk; P  [(R/d3Jc2)]Ba4 for Ba<< Bc=m0Jcd/2P  JcRBa for Ba>>Bc where Jc(B) = Jc(0) critical current density, R = radius, and d = thickness. ac losses/ volume J. R. Clem and A. Sanchez, PRB 50, 9355(1996).

  6. #1 Ba4 0.5 mm #2 Magneto-optical Images from #1 and 2 YBCO films at 60 K ac losses from YBCO (disc) films on SrTiO3 in perpendicular magnetic fields #1 film #2 film YBCO disk shaped films on SrTiO3: 1mm thick; ~ 5 mm dia;. T = 77 K. Qiang Li and Z. Ye

  7. ac losses in YBCO (disc) films in perpendicular magnetic fields QN(Ba) = [losses /(pBa2/m0)] (3pd/8R) Theories: The Bean Jc model: Jc(B) = Jc(0) J. R. Clem and A. Sanchez, PRB 50, 9355(1996). The Kim Jc model: Jc(Ba)=Jc(0)/(1+Ba/B0K) D. V. Shantsev, et al., PRB 61, 9699 (2000). Brookhaven Science Associates U.S. Department of Energy

  8. Oxide buffer (0.3 mm) YBCO (0.8 mm) Ni-5at. %W (75 mm) 5 mm Brookhaven Science Associates U.S. Department of Energy ac losses in YBCO films in perpendicular magnetic fields Effects of magnetic substrates From AmSC Tc ~ 300 K. Relative permeability mr = m/m0 ~ 2.5 Magneto-optical image showing macroscopically uniform flux penetration

  9. Brookhaven Science Associates U.S. Department of Energy Effects of stacking tapes H YBCO/Ni-W AMSC 2nd batch B3 B4 Theory for single film with equivalent thickness

  10. H a a b b c c Brookhaven Science Associates U.S. Department of Energy Effects of magnetic substrates (Ni-W) YBCO/Ni-W (AMSC) B3 [P(B)/B2]

  11. Brookhaven Science Associates U.S. Department of Energy Deviations of the loss characteristics from those of a YBCO film on a non-magnetic substrate • Magnetic field dependence at low fields: • P(B) B3 rather than B4(for a non-magnetic substrate) • The thickness dependence: • P(2 disks)/P(1 disk) ~ 0.54instead of(1/t3) = 1/8(for a nonmagnetic substrate)

  12. images of a superconductor Soft magnet d H superconductor Soft magnet W Brookhaven Science Associates U.S. Department of Energy YBCO on a buffered magnetic substrate: Magnetic mirror effect Genenko, et al., PR B 62, 3453 (2000)

  13. z d t x W Brookhaven Science Associates U.S. Department of Energy YBCO on buffered magnetic substrates: ac losses of a virtual-infinite-film stack For an infinite stack of superconductors, if d/W << 1, ac losses  B3/Jc(ave) B3/t In the present case, d/W ~ 5x10-5. Y. Mawatari, IEEE Trans. on Appl. Supercond. 7, 1216 (1997); PR B54, 13215 (1996). H

  14. Brookhaven Science Associates U.S. Department of Energy Deviations of the loss behaviors from those of YBCO on non-magnetic substrates • Magnetic field dependence: • P(B) B3 rather than B4 , butforan infinite stack  B3 • The thickness effects: • P(2 disks)/P(1 disk) ~ 0.54 instead of(1/t3) = 1/8, • butfor an infinite stack  (1/t) = 0.5.

  15. Brookhaven Science Associates U.S. Department of Energy Effects of stacking tapes H YBCO/Ni-W AMSC 2nd batch B3 Nonmagnetic substrate: M. Iwakuma, K. Toyota, M. Nigo, T. Kiss, K. Funaki, Y. Iijima, T. Saitoh, Y. Yamada, and Y. Shiohara, Physica C, 412 – 414, 983 (2004).

  16. magnet Jc sc Bz R J c J B B 0 a a R Brookhaven Science Associates U.S. Department of Energy ac losses in YBCO (disc) films : YBCO on buffered magnetic substrates sc H

  17. Brookhaven Science Associates U.S. Department of Energy Magnetic material Finite element calculations: superconductor (a) B = Bfp superconductor H (b) Magnetic material superconductor S. Farinon, et al., IEEE trans. on Appl. Supercondd. 15, 2867 (2005)

  18. A disk/strip z H sc Magnetic substrate J c J B B a a R Implication to self-field critical transport currents of superconducting films on a magnetic substrate Jc currents Magneto-imaging of a YBCO strip showed not peaking of B at the edges. magn. fields Bz 0 R Brookhaven Science Associates Department of Energy

  19. z Magnetic substrate t d x W Implication to self-field critical transport currents of superconducting films on a magnetic substrate sc B • The critical currents of sc films on a magnetic substrate will “not” be same as those of the same films on a nonmagnetic substrate. This is because the demagnetizing effect of a current carrying film will be reduced significantly if the film is on a magnetic substrate. W Brookhaven Science AssociatesDepartment of Energy

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