  We analyze the fast-moving string in the magnetic Melvin field background and
find that the associated effective Lagrangian of string sigma model describes
the spin chain model with external magnetic field. The spin vector in the spin
chain has been properly deformed and is living on the deformed two-sphere or
deformed two-dimensional hyperboloid, depending on the direction around which
the string is spinning. We describe in detail the characters of spin
deformation and, in particular, see that this is a general property for a
string moving in a class of deformed background.
