  The magnetocaloric effect in single crystalline Nd_{0.7}Sr_{0.3}MnO_{3} is
investigated by measuring the field-induced adiabatic change in temperature
which reveals a single negative peak around 130 K well below the Curie
temperature (T_C=203 K). In order to understand this unusual magnetocaloric
effect, we invoke the reported {55}^Mn spin-echo nuclear magnetic resonance,
electron magnetic resonance and polarized Raman scattering measurements on
Nd_{0.7}Sr_{0.3}MnO_{3}. We show that this effect is a manifestation of a
competition between the double exchange mechanism and correlations arising from
coupled spin and lattice degrees of freedom which results in a complex
ferromagnetic state. The critical behavior of Nd_{0.7}Sr_{0.3}MnO_{3} near
Curie temperature is investigated to study the influence of the coupled degrees
of freedom. We find a complicated behavior at low fields in which the order of
the transition could not be fixed and a second-order-like behavior at high
fields.
