Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Flux structures in mesoscopic YBa2CU3O7-delta discs
AU - Crisan, A
AU - Bending, SJ
AU - Pross, A
AU - Aziz, A
AU - Grigorenko, AN
AU - Humphreys, RG
PY - 2005/3
Y1 - 2005/3
N2 - Scanning Hall probe microscopy has been used to study flux Structures and dynamics in 5 mu m x 5 mu m YBCO thin film squares, which are mesoscopic with respect to the magnetic penetration depth, lambda(T), at temperatures close to T-C. A number of unusual vortex phenomena are observed in these microstructures which differ qualitatively from the expected behaviour of more macroscopic pieces of film. In field-cooled (FC) experiments to similar to 65 K a full Meissner state is generated for cooling fields less than similar to 6 Oe, reflecting the relatively small demagnetization factors in our samples. Cooling in higher fields, however, results in only a very weak diamagnetic response at low temperatures whose magnitude is almost independent of the cooling field. In contrast we observe considerable trapped flux upon field-removal whose magnitude grows monotonically with cooling field. Remarkably, all FC flux distributions exhibit almost perfect rotational symmetry, and can be nearly completely cancelled in a reversible fashion by tuning the field applied to the initially FC state. Our field-cooled and zero-field-cooled results have been analysed in terms of a Bean-like critical state model containing constant edge and bulk current densities, and most of the observed phenomena can be explained by considering the relative weight of these two components. Not all flux profiles call be described by our simple model, however, and under certain circumstances symmetry-breaking 'dipole'-like flux structures can form in several adjacent YBCO squares. We speculate that these are related to the unidirectional At-ion milling process which was used to pattern the squares and could have broken the expected four-fold symmetry. We note that our results could have important implications for the miniaturization of thin film HTS devices.
AB - Scanning Hall probe microscopy has been used to study flux Structures and dynamics in 5 mu m x 5 mu m YBCO thin film squares, which are mesoscopic with respect to the magnetic penetration depth, lambda(T), at temperatures close to T-C. A number of unusual vortex phenomena are observed in these microstructures which differ qualitatively from the expected behaviour of more macroscopic pieces of film. In field-cooled (FC) experiments to similar to 65 K a full Meissner state is generated for cooling fields less than similar to 6 Oe, reflecting the relatively small demagnetization factors in our samples. Cooling in higher fields, however, results in only a very weak diamagnetic response at low temperatures whose magnitude is almost independent of the cooling field. In contrast we observe considerable trapped flux upon field-removal whose magnitude grows monotonically with cooling field. Remarkably, all FC flux distributions exhibit almost perfect rotational symmetry, and can be nearly completely cancelled in a reversible fashion by tuning the field applied to the initially FC state. Our field-cooled and zero-field-cooled results have been analysed in terms of a Bean-like critical state model containing constant edge and bulk current densities, and most of the observed phenomena can be explained by considering the relative weight of these two components. Not all flux profiles call be described by our simple model, however, and under certain circumstances symmetry-breaking 'dipole'-like flux structures can form in several adjacent YBCO squares. We speculate that these are related to the unidirectional At-ion milling process which was used to pattern the squares and could have broken the expected four-fold symmetry. We note that our results could have important implications for the miniaturization of thin film HTS devices.
KW - HALL PROBE MICROSCOPY
KW - PENETRATION
KW - STATE
KW - STRIP
KW - SUPERCONDUCTING DISK
KW - PHASE-TRANSITIONS
KW - THIN-FILM
KW - ANTIVORTICES
KW - MAGNETIC-FIELD
U2 - 10.1088/0953-2048/18/3/001
DO - 10.1088/0953-2048/18/3/001
M3 - Journal article
VL - 18
SP - 207
EP - 213
JO - Superconductor Science and Technology
JF - Superconductor Science and Technology
SN - 1361-6668
IS - 3
ER -