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Off-axis MgB2 films using an in situ annealing pulsed laser deposition method
Highly smooth and c-axis oriented superconducting MgB2 thin films were
prepared by pulsed laser deposition (PLD) with off-axis geometry. The films
were deposited on Al2O3-C substrates perpendicularly aligned to a
stoichiometric MgB2 target in a 120 mTorr high purity Ar background gas. An in
situ annealing was carried out at 650C for 1 min in a 760 Torr Ar atmosphere.
Despite the short annealing time, an x-ray theta-2 theta scan shows fairly good
crystallization, according to the clear c-axis oriented peaks for the films.
Both atomic force microscopy and the x-ray diffraction results indicate that
the crystallite size is less than 50nm. The root mean square roughness of our
off-axis film is ~4 nm in a 5x5 square micron area. The Tc onset value of the
best off-axis film reaches 33.1 K with a narrow transition width of 0.9 K. The
films showed no anisotropy in Hc2-T curves when parallel and perpendicular
fields were applied. The slope of Hc2-T curves in low field regime is 1 T/K,
which is among the highest reported values.Comment: 7 pages 7 figure
Comparative study of in situ and ex situ MgB2 films deposited by pulsed laser deposition
Two types of MgB2 films were prepared by pulsed laser deposition (PLD) with
in situ and ex situ annealing processes respectively. Significant differences
in properties between the two types of films were found. The ex situ MgB2 film
has a Tc of 38.1K, while the in situ film has a depressed Tc of 34.5K. The
resistivity at 40K for the in situ film is larger than that of the ex situ film
by a factor of 6. The residual resistivity ratios (RRR) are 1.1 and 2.1 for the
in situ and ex situ films respectively. The Jc-H curves of the in situ film
show a much weaker field dependence than those of the ex situ film,
attributable to stronger flux pinning in the in situ film. The small-grain
feature and high oxygen level may be critical for the significant improvement
of Jc in the in situ annealed MgB2 film.Comment: 6 pages, 6 figure
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