  The in situ annealing conditions of pulsed laser deposited MgB2 films were
studied. The precursor films were deposited at 250 C from a stoichiometric MgB2
target in a 120mTorr Ar atmosphere. The films were then in situ annealed at a
temperature from 450 C to 800 C and an annealing time from 1 minute to 10
minutes. We found that the superconducting properties depend in a crucial way
on the annealing conditions: temperature, heating rate and time. The best film
with a thickness of ~600nm was obtained under the following annealing
conditions: Tanneal=680-690 C, tanneal=1 min, heating rate= 38 C/min. The Tc
onset of the film is 28K with a transition width of ~10K. The hysteresis loop
of magnetic moment of the film indicates weak field dependence in high fields.
Magneto-optical imaging of the film showed quite homogeneous magnetic flux
penetration, indicating structural homogeneity. The films without annealing
showed no superconductivity.
