FERROMAGNETIC-RESONANCE AND MAGNETIC HOMOGENEITY IN A GIANT-MAGNETORESISTANCE MATERIAL LA2 3BA1/3MNO3/

Systematic magnetization, resistivity, and ferromagnetic resonance mea surements have been done on bulk as well as thin-film samples of La2/3 Ba1/3MnO3. Bulk specimens and as-grown films show broad lines whose wi dth increases to nearly 1 kOe as T is reduced to 77 K. At low T, the b ulk magnetization is as expected for fully aligned spins [4 pi M(0) = 7.2 kOe]. As-grown films, however, show somewhat smaller values. The m ain finding is that films which have been annealed for several days at 1000 degrees C in an atmosphere of O-2 exhibit narrow (similar to 200 Oe at 10 GHz) linewidths which are effectively independent of tempera ture. These are, to our knowledge, the narrowest lines observed in gia nt magnetoresistance materials, a strong indication of homogeneity. Th e low-T magnetization is near the expected value, and its temperature dependence is highly suggestive of low-lying spin-wave excitations.