of Spontaneous and field-induced

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1 Magneto-Optics of Spontaneous and field-induced induced Vortices in twinned YBa 2 Cu 3 O 7-δ /La 1-x Sr x MnO 3 bilayers Superconductivity Group (Politecnico di Torino): Roberto Gerbaldo, Gianluca Ghigo, Laura Gozzelino, Francesco Laviano Enrica Mezzetti, Bruno Minetti in collaboration with Piotr Przyslupski, Andrei Tsarou, Andrzej Wisniewski Polish Academy of Sciences, Institute of Physics, Al. Lotnikov 32/46, Warsawa Poland

2 Outline Magneto-optical technique a very brief survey Magnetic Phase Diagram of the Manganite compound: different dopings examined (comparison between La and Nd manganites) Interaction between Vortices and Magnetic Structures in YBCO/LSMO bilayers: vortex channeling and controlled guidance Magnetic Imaging of Domain and Domain-walls in Manganite films on twinned substrates Preliminary results on magneto-optical imaging of the magnetic pattern in Cobaltite crystals

3 Magneto-optical optical technique The Faraday effect M. Faraday, Trans. Roy. Soc. 146 (1846) 1 The polarization plane of the light refracted by the ferrite is rotated by an angle (α F ) proportional to the lenght of the light path into the medium and to the local magnetization component along the light direction. F.Laviano, D. Botta, A. Chiodoni, R. Gerbaldo, G. Ghigo, L. Gozzelino, S. Zannella and E. Mezzetti, Supercond. Sci. Technol., 16 (2003) 71

4 Superconductor/Manganite Heterostructures La 1-x Sr x MnO Atomic structure close to a cubic perovskite a ~ nm YBa 2 Cu 3 O 7-δ Orthorombic structure a = nm b = nm c = nm P. Przyslupski et al. J. Appl. Phys. 95 (2004) Good matching between manganite and high-t c cuprate lattices high quality heterostructure TEM image of [LSMO x 8 u.c. /YBCO x 3 u.c.] superlattice

5 A.P. Ramirez, J. Phys.: Condens. Matter 9 (1997) Magnetic Phase Diagram of Sr-doped Manganite compunds: : LSMO Manganite film magnetization strongly depends on Strontium doping level YBCO LSMO LaAlO 3 YBCO thickness: : 50 nm LSMO thickness: : 100 nm grown by multitarget sputtering * * P. Przyslupski et al. IEEE Trans. Appl. Supercond. 7 (1997) 2192 La Sr 0.33 MnO 3 Ferromagnetic, metallic phase with curie = 360 K T curie

6 Magnetic Phase Diagram of Sr-doped Manganite compunds: : LSMO Manganite film magnetization strongly depends on Strontium doping level YBCO LSMO LaAlO 3 YBCO thickness: : 50 nm LSMO thickness: : 100 nm grown by multitarget sputtering * * P. Przyslupski et al. IEEE Trans. Appl. Supercond. 7 (1997) 2192 A.P. Ramirez, J. Phys.: Condens. Matter 9 (1997) La Sr MnO 3 Ferromagnetic insulator phase with T Curie = 180 K

7 Magnetic Phase Diagram of Nd-doped doped Manganite compunds: : NSMO Manganite film on Nd doping level film magnetization strongly depends YBCO NSMO LaAlO 3 YBCO thickness: : 50 nm NSMO thickness: : 100 nm grown by multitarget sputtering * * P. Przyslupski et al. IEEE Trans. Appl. Supercond. 7 (1997) 2192 For 0.5 Nd doping level the ground state at low temperature is antiferromagnetic!

8 Magneto-optical optical Imaging of La on twinned LaAlO 3 La Sr 0.33 MnO MnO 3 Optical image T = 300 K 0 < H [110] < 500 Oe Magneto-Optics 300 µm 300 µm Tri-crystal point Twinned structure in LAO Multi-domain magnetic pattern in LSMO LaAlO 3 Twin Boundaries induce splitting of Manganite Magnetic Domains and out-of of-plane Domain-Walls alls (DW s)) are present

9 Domains and Domain-walls in La on twinned LaAlO 3 La Sr 0.33 MnO MnO 3 T = 100 K 0 < H [110] < 500 Oe Patterns obtained by saturating the magnetization with an in-plane magnetic field in the (110) direction Out of plane magnetic moments ( DW, i.e. B z ) 200 µm 200 µm Out of plane magnetic moments ( DW, i.e. B z ) Magnetic domain pattern is stable for T < T Curie Domains with in plane magnetization

10 Spontaneous Vortex Phase in YBa 2 Cu 3 O 7-δ / La MnO 3 bilayer 200 µm La Sr 0.33 MnO T = 4.2 K µ 0 H a = 0 mt ZERO FIELD COOLING When cooling below YBCO T c, T=4.2K mt vortex-antivortex rows are spontaneously nucleated on out-of-plane magnetic domain walls (DWs) and they stay pinned at the DW locations B z (brigth DW) sample edge 0-2 B z (dark DW) = B z ~ 2.5 mt (i.e. 0.6 vortices/µm 2 inside DW) F. Laviano, L. Gozzelino, E. Mezzetti, P. Przyslupski, A. Tsarou, A. Wisniewski, Lett. 86, (2005) Appl. Phys. Lett.

11 Vortex Channelling in YBa 2 Cu 3 O 7-δ /La MnO 3 bilayer /La Sr 0.33 MnO Perpendicular vortex motion to YBCO twin-boundaries (magnetized by the underlying locked DWs) T = 4.2 K µ 0 H z = 3 mt 4.0 Flux quanta pile up on 3.5 DW DWs of the same 3.0 vorticity,, increasing the 2.5 local flux density DW (brighter lines), or 1.0 partially position (µm) DWs of opposite sign (darker lines). B z (mt) partially annihilate on 200 µm mt B z [(µ 0 H a = 3 mt) (µ 0 H a = 0 mt)] DWs perpendicular to the vortex motion direction always slow down the vortex diffusion process

12 Vortex Guidance in YBa 2 Cu 3 O 7-δ /La MnO 3 bilayer /La Sr 0.33 MnO Parallel vortex motion to YBCO twin-boundaries (magnetized by the underlying locked DWs) T = 4.2 K vortices diffusing parallel to DWs are affected by a two-fold channeling phenomena flux diffusion is enhanced for vortices of the same polarization of DWs depressed for vortices with opposite sign with respect to DWs guidance longitudinal TBs with respect to the Lorentz drag force F. Laviano et al. Appl. Phys. Lett. 86, (2005) Controlled Guidance of the flux quanta movement and arrangement towards vortex magnetic memory

13 Comparison with the electrodynamics of YBa 2 Cu 3 O 7-δ / Nd 0.5.5Sr 0.5 MnO 3 bilayer 15.7 Oe T = 4.2 K 46.4 Oe None flux trapped on cooling TB s act only as very good pinning defects

14 Spontaneous Vortex Phase in YBa 2 Cu 3 O 7-d / La MnO 3 bilayer Optical image La Sr MnO when cooling below YBCO T c in zero applied field, vortex-antivortex singularities are spontaneously nucleated along the out-of-plane magnetic domains Magneto-Optics 50 µm Trapped Vortex Density B z (brigther domains) B z (darker domains) = B z ~ 0.6 mt (i.e vortices/µm 2 along the domains) T = 4.2 K µ 0 H a = 0 mt ZERO FIELD COOLING Lower vortex density is induced with respect to La Sr 0.33 MnO 3 Sr 0.33

15 Vortex Channeling in YBa 2 Cu 3 O 7-d / La MnO 3 bilayer La Sr MnO Magnetic Domains affects the Vortex Motion: longitudinal and transversal channelling occur at DW s T = 4.2 K µ 0 H z = 4.5 mt T = 4.2 K µ 0 H z = 7.5 mt 50 µm 20 µm Magneto-optical frame

16 Interaction of Vortices and Magnetic Domains in YBa 2 Cu 3 O 7-d / La Sr MnO 3 bilayer B z (mt) sample sample edge edge TB's α position (µm) Sr Magnetic domain influence on the critical state pattern: the flux gradient seems to be periodically modulated with discontinuities at TB s locartions γ T = 4.2 K µ 0 H z = 4.5 mt β α β γ 50 µm the vortex guidance over an extend domain is isotropic L. Gozzelino et al., Supercond. Scie. Technol., 19 (2006) S50 mt

17 J r (10 10 A/m 2 ) Local Supercurrent Imaging in YBa 2 Cu 3 O 7-d / La MnO 3 bilayer position(µm) La Sr MnO T = 4.2 K µ 0 H z = 4.5 mt A/m J -1.5 r J 50 µm φ MOI A/m 2 Spontaneous vortex-phase phase induces supercurrent modulations inside the Meissner state (S.( Erdin, I.F. Lyuksyutov, V.L. Pokrovsky, and V.M. Vinokur, PRL88(2002)017001)

18 Interaction between YBCO and LSMO J c ~ 8% Local Supercurrent Modulations MOI A/m J c ~ A/m 2 supercarrier density is locally modulated by the magnetic domainwall structure position (µm) J 50 µm T = 4.2 K µ 0 H z = 4.5 mt Local J depletion in correspondence of DW s J (10 11 A/m 2 )

19 Domains and Domain-walls in.885sr MnO 3 on twinned LaAlO 3 La Sr Different Magnetization states in the Ferromagnetic Insulator (FI) phase (T curie ~180 K, applied field at T~4K) 180 Bloch Walls of manganite are visible in between the DW s pinned at the twin-boundaries (TB s), the roughness is due to the energy minimization of the DW s T = 3.8 K H [111] 10kOe mm µm 5 µm

20 Conclusions Magneto-optical optical imaging of magnetic patterns in manganite film with different dopings and manganite/superconductor heterostructures: 1. influence of the substrate structure 2. Spontaneous Vortex Phase: magnetic pattern freezed in the superconductor 3. Vortex channeling -> controlled guidance of vortices by magnetic domains and domain-walls Supercurrent imaging allows observing the local electromagnetic coupling in the superconducting/magnetic bilayers (in progress ) Imaging the Domain Wall dynamics, in manganite films with TB s, reveals the way to engineer the local coercitivity of the material by suitable defects and magnetic fields

21 Thanks for your attention!!!