INTERLAYER%20EXCHANGE%20COUPLING,%20PAIR%20BREAKING%20

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INTERLAYER EXCHANGE COUPLING, PAIR BREAKING 2D
VORTEX DYNAMICS IN FERROMAGNET-SUPERCONDUCTOR
HETEROSTRUCTURES
R. C. BUDHANI Indian Institute of Technology,
Kanpur
Collaborator - K. Senapati Funding - D.R.D.O.
Govt. of India
Objectives -
Pair-breaking effects of ferromagnetic boundaries
in cuprates. Influence of ferromagnetic
boundaries on the vortex state of ultra-thin YBCO
films. Exchange coupling between two ferromagnets
separated by an exotic superconductor.
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THIN FILM STRUCTURES
dFM --- 300 Å dY --- 50 - 500 Å dNM --- 100 Å
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- STATE OF MAGNETIZATION IN LSMO-
MS(T)/MS(0) 1 - AT3/2 ?
J 2 meV
Soft Magnetic Films with in-plane Magnetization
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MOST OF THE DYNAMICS SCALES WITH THE EFFECTIVE
THICKNESS
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- VORTEX DYNAMICS -
Senapati et al. Rev. Sci. Instrum. 75, 141 (2004)
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Tirr ? Tc(H) Critical temperature at which ?ac?
? Loss of pinning ? Loss of phase stiffness
Clean limit pair breaking
HPB(0) scales with deff
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Two regimes of thermal activation separated by a
characteristic temperature T
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High T (gt T) --------- U0(T) ? Energy of
creation of dislocations Low T (lt T) ---------
U0(T) ? Energy required to move preexisting
dislocations
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Summary

• The dynamics of the vortex state in 2D films of
  YBCO sandwiched between FM-boundaries has been
  studied over a wide range of temperature,
  frequency and magnetic field strength.
• Flux motion is controlled by creation of
  dislocations near Tm, and by the motion of
  preexisting dislocations at TltTm.
• The irreversibility temperature in the vortex
  state maps onto a clean-limit pair-breaking
  temperature Tc(H), and the pair-breaking field
  scales with the thickness of the films.

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LSMO YBCO LSMO (300 Å) (100 Å) (300 Å)
M-H curves Tc 62 K
K. Senapati and R. C. Budhani, Submitted to Phys.
Rev. B.