Ferromagnetic resonance and magnetization studies on ferrimagnetic double perovskites A(2)FeReO(6) (A = Ca, Sr, Ba)

We present the results of an investigation of the magnetic properties A(2)F eReO(6) (A = Ca, Sr, Ba). We have studied the magnetization, high-temperatu re susceptibility and the ferromagnetic resonance response. The Ba and Sr s ystems are conducting while the Ca material is an insulator. The ordering t emperature of the Ca materials is highest (similar to 540 K) and decreases to 315 K for the Ba system. The high-temperature susceptibilit suggests a l arge moment, and the Curie-Weiss temperature is very close to the ordering temperature, as expected for a simple ferromagnet, although the ferromagnet ic moment is somewhat less than expected. The spin dynamics are rather pecu liar: the ferromagnetic resonance results suggest a magnetically inhomogene ous material. We discuss these results in terms of cation disorder.