  The response of spinor Bose-Einstein condensates to dynamical modulation of
magnetic fields is discussed with linear response theory. As an experimentally
measurable quantity, the energy absorption rate (EAR) is considered, and the
response function is found to access quadratic spin correlations which come
from the perturbation of the quadratic Zeeman term. By applying our formalism
to spin-1 condensates, we demonstrate that the EAR spectrum as a function of
the modulation frequency is able to characterize the different magnetically
ordered phases.
