  By measuring the magnetization hysteresis loops of superconducting
Ba0.6K0.4Fe2As2 single crystals, we obtained the high upper critical field and
large current carrying ability, which point to optimistic applications. The
fishtail (or second peak) effect is also found in the material, and the
position of the vortex pinning force shows a maximum at 1/3 of the reduced
field, being consistent with the picture of vortex pinning by small size normal
cores in the sample. Together with the resistive measurements, for the first
time the vortex phase diagram is obtained for superconductor Ba0.6K0.4Fe2As2.
