Ferromagnetic resonance and magnetic homogeneity in a giant-magnetoresistance material La23Ba13MnO3

Systematic magnetization, resistivity, and ferromagnetic resonance measurements have been done on bulk as well as thin-film samples of La23Ba13MnO3. Bulk specimens and as-grown films show broad lines whose width increases to nearly 1 kOe as T is reduced to 77 K. At low T, the bulk magnetization is as expected for fully aligned spins [4πM(0)=7.2 kOe]. As-grown films, however, show somewhat smaller values. The main finding is that films which have been annealed for several days at 1000 °C in an atmosphere of O2 exhibit narrow (∼200 Oe at 10 GHz) linewidths which are effectively independent of temperature. These are, to our knowledge, the narrowest lines observed in giant magnetoresistance materials, a strong indication of homogeneity. The low-T magnetization is near the expected value, and its temperature dependence is highly suggestive of low-lying spin-wave excitations.