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R. C. B UDHANI Indian Institute of Technology, Kanpur

I NTERLAYER E XCHANGE C OUPLING , P AIR B REAKING & 2D V ORTEX D YNAMICS IN F ERROMAGNET -S UPERCONDUCTOR H ETEROSTRUCTURES. R. C. B UDHANI Indian Institute of Technology, Kanpur. Collaborator :- K. Senapati Funding :- D.R.D.O. Govt. of India. Objectives :-.

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R. C. B UDHANI Indian Institute of Technology, Kanpur

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  1. INTERLAYER EXCHANGE COUPLING, PAIR BREAKING & 2D VORTEX DYNAMICSIN 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.

  2. dFM dNM LSMO PBCO dY dY YBCO (c-axis) YBCO (c-axis) dFM dNM LSMO PBCO [100] STO [100] STO THIN FILM STRUCTURES dFM --- 300 Å dY --- 50 - 500 Å dNM --- 100 Å

  3. -: STATEOFMAGNETIZATIONINLSMO:- MS(T)/MS(0) = 1 - AT3/2  J ~ 2 meV Soft Magnetic Films with in-plane Magnetization

  4. Effective Tc due to pair breaking (PB) • Inhomogeneous stress field • Hole concentration • Reduced Tc Exchange field Spin injection Interface transparency Enhanced PB in a reduced carrier system MOST OF THE DYNAMICS SCALES WITH THE EFFECTIVE THICKNESS

  5. Superconducting magnet Vacuum can Drive coil Sample Hall sensor G-10 base Brass rod Irreversibility temperature and field  TH3 Heating element Inverse sheet inductance (1/L)  TH’ TH’ = 1- (4a2/c2d) (1/L) [d = thickness , a = effective radius] 1/L =  ln(1/Z) THERMALLY ACTIVETED INVERSE SHEET INDUCTANCE -: VORTEX DYNAMICS :- Senapati et al. Rev. Sci. Instrum. 75, 141 (2004)

  6. Tirr Tc(H) Critical temperature at which ac  Loss of pinning  Loss of phase stiffness Clean limit pair breaking : HPB(0) scales with deff

  7. LSMO-YBCO-LSMO Frequency : 121 Hz PBCO-YBCO-PBCO Frequency : 121 Hz Two regimes of thermal activation separated by a characteristic temperature T*

  8. High T (> T*)--------- U0(T)  Energy of creation of dislocations Low T (< T*) --------- U0(T)  Energy required to move preexisting dislocations

  9. 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 T<Tm. • 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.

  10. 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.

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