INVESTIGADORES
BEKERIS Victoria Isabel
congresos y reuniones científicas
Título:
Arrays of artificial magnetic pinning centers for vortex matter
Autor/es:
V. BEKERIS , C. CHILIOTTE, D. PÉREZ DAROCA , G. PASQUINI1, M. OLIVA , C.-P. LI , F. CASANOVA3, J. E. VILLEGAS AND I. K. SCHULLER
Lugar:
Valparaiso
Reunión:
Workshop; Sólidos 2009; 2009
Institución organizadora:
Universidad de Valparaiso
Resumen:
It is
well known that the introduction of periodic arrays of well defined
pinning centers in superconducting samples can reduce vortex mobility,
giving rise to higher critical currents. Basically there are two ways
to artificially control vortex pinning: by
suppression of the superconducting order parameter thus generating a
minimum in the self energy of the vortex line, or by lowering the
magnetic energy of the system by modulation of the magnetic field. The
progressive development of material deposition
techniques and self organization, have made it possible to fabricate
superconductor-ferromagnet artificial structures at nanometer scales,
which is the scale of the relevant superconducting parameters that
intervene in vortex pinning phenomena. In this work we study the pinning
effects of magnetic nano particles arrayed periodically and close to a
superconducting film. As ferromagnetic materials in close contact to
superconducting materials induce proximity effect, pinning effects
could be related to suppression of the order parameter and to magnetic
field modulation. In order to study the effect of both contributions, we have studied dc and ac magnetic properties of superconducting Nb films either deposited on top of an array of Fe nanoparticles or deposited on top of a SiO2 buffer layer 100 nm thick separating the superconducting film from the nanoparticles, to avoid proximity effects.
We present preliminary results on ac susceptibility, c (H,T) and dc magnetization, M(H,T), of Nb films (~100 nm thick), prepared as described elsewhere [1], deposited on top of a triangular array of sub-micrometric magnetic Fe particles ~
120 nm apart. M(H) results indicate that the particles are in
magnetic vortex state with remanent magnetization oriented
perpendicular to the film surface. FORC diagrams in the normal state
indicate that interactions between magnetic dots are weak. Samples
where proximity effect is expected to contribute, show wide
superconducting transitions and matching filed effects are not as sharp
as in samples where the effect has been reduced by a separating
isolating layer. Additionally, we observe in c (H,T) response, a distinct hysteretical behavior, still not well understood. We acknowledge contributions from grants UBACyT EX 13.
[1] Chang-Peng Li et. al., J. Appl. Phys. 100 074318 (2006).