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, (06)
Brookhaven
Science Associates
U.S. Department of Energy 1

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, ).
3) Implication to the transport self-field Jc of superconducting films on a magnetic substrate
Brookhaven
Science Associates
U.S. Department of Energy 1

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

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

5. ac losses in YBCO films in perpendicular ac magnetic fields
1) a cylinder:
P  (1/JcR)Ba for Ba << Bp=2m0JcR P  JcRBa for Ba >> Bp
2) a thin disk;
P  [(R/d3Jc2)]Ba4 for Ba<< Bc =m0Jcd/2 P  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).
U.S. Department of Energy
Brookhaven Science Associates 1

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

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

9. Effects of stacking tapesH
YBCO/Ni-W AMSC 2nd batch B3 B4
Theory for single film with equivalent thickness
Brookhaven Science Associates
U.S. Department of Energy 1

10. Effects of magnetic substrates (Ni-W)
YBCO/Ni-W (AMSC) H b c a a b c B3
[P(B)/B2]
Brookhaven Science Associates
U.S. Department of Energy 1

11. 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) ~ 0.54 instead of (1/t3) = 1/8 (for a nonmagnetic substrate) 
Brookhaven
Science Associates
U.S. Department of Energy

12. YBCO on a buffered magnetic substrate: Magnetic mirror effect
superconductor
Soft magnet W d
images of a superconductor H
Genenko, et al., PR B 62, 3453 (2000)
Brookhaven Science Associates
U.S. Department of Energy 1

13. YBCO on buffered magnetic substrates: ac losses of a virtual-infinite-film stackW d t z x
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, (1996).
H 
Brookhaven Science Associates
U.S. Department of Energy

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

15. Effects of stacking tapesH
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).
Brookhaven Science Associates
U.S. Department of Energy 1

16. ac losses in YBCO (disc) films : YBCO on buffered magnetic substratesH a R B J c Bz Jc
Brookhaven Science Associates
U.S. Department of Energy 1

17. Finite element calculations:
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)
Brookhaven Science Associates
U.S. Department of Energy

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

19. Brookhaven Science Associates Department of Energy
Implication to self-field critical transport currents of superconducting films on a magnetic substrate sc W d t z x
Magnetic substrate 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 Associates Department of Energy