Magnetic field effects in the dynamics of alternating or anisotropic quantum spin chains

This is a study of magnetic-field effects on various zero-temperature properties of the one-dimensional S = 12 XY model with exchange alternation or anisotropy. Alternation and anisotropy in the interaction cause different types of spin ordering in the ground state, which in turn are responsible for characteristic effects in various physical properties. The presence of an external magnetic field perpendicular to the XY-plane has the tendency to counteract these orderings. The latter are suppressed when the field reaches a critical strength.