set term x11
bin_width=10
time_binning_start=500.
do for [index=300:2000]{
print 'index=',index,'  time=',index*bin_width+time_binning_start
plot  'spin_vs_momentum_at_time.dat' using 3:4:6 i index:index w e,'' u 3:7 i index:index w l
pause -1
}