Possible inverse melting of vortex lattice in high-

Using molecular-dynamic simulations for a vortex lattice with random pinning, thermal fluctuations and vortex-vortex interactions, we study the order-disorder transition from a Bragg glass (BG) to an amorphous vortex glass (VG) or a vortex liquid (VL) in the pinning strength-temperature phase diagram. The order-disorder transition line is determined by calculating the static structure factor of vortex lattice and the finite-size exponent. A portion of the BG region is found to be sandwiched in between the VG phase at lower temperatures and VL phase at higher temperatures, exhibiting inverse melting behavior observed recently on $\chem{Bi_2Sr_2CaCu_2O_8}$ crystals by Avraham et al. (Nature, 411 (2001) 451). This unusual behavior is attributed to the temperature-enhanced interaction between vortices