Magnetization dynamics in La_0.67Ca_0.33MnO₃ epitaxial films probed with resonant and non-resonant microwave absorption

Temperature (T) dependent microwave absorption measurements are performed on La_0.67Ca_0.33MnO₃ (LCMO) epitaxial thin films of thickness 100 and 200-nm in an electron paramagnetic resonance spectrometer operating in X-band. The resonant absorption peak is monitored for out-of-plane (H ⊥) and in-plane (H ∥) dc magnetic field (H) as the system goes through magnetic ordering. These data suggest a resilient transformation to the ferromagnetic (FM) phase in the vicinity of the Curie temperature (T_C), indicative of a phase separation, which is dominant in the thinner film. The saturation magnetization is calculated from SQUID magnetometry on the same film. A pronounced zero-field absorption is seen in H ∥ geometry displaying anomalous growth in 100-nm film at T-<-T_C. This feature is correlated with the magneto-conductivity of the manganite which is colossal in the vicinity of T_C in the well-ordered film of thickness 200-nm. Signature of standing spin wave modes is seen in H ⊥ measurements which are analyzed to calculate the spin wave stiffness constant D(T) in the limit of zero temperature. The same is also inferred from the decay of equilibrium magnetization in the framework of Bloch law. These studies reveal that a bulk like LCMO is obtained in the fully relaxed thicker films.