Temperature and field dependence of microwave losses in manganite powders

We report systematic measurements of the temperature and field dependence o f microwave losses in micron-size powders (similar to 3 mu m) of the mangan ites Nd0.7Sr0.3MnO3, La0.7Ca0.3MnO3, La0.8Ba0.2MnO3, and La1.4Ca1.6Mn2O7. W e fully confirm previous findings of a large increase in zero-field absorpt ion, in La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3, accompanying the onset of ferrom agnetism and a concomitant colossal low-field magnetoimpedance (up to 80% a t 600 Oe at room temperature). An oversimplified set of computations render s plausible support for interpreting these observations as arising from abs orption in the spin system. Possible applications of these novel phenomena are also described. (C) 1999 American Institute of Physics. [S0021-8979(99) 05814-4].