Temperature and field dependence of microwave losses in manganite powders

We report systematic measurements of the temperature and field dependence of microwave losses in micron-size powders (∼3 μm) of the manganites Nd0.7Sr0.3MnO3, La0.7Ca0.3MnO3, La0.8Ba0.2MnO3, and La1.4Ca1.6Mn2O7. We fully confirm previous findings of a large increase in zero-field absorption, in La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3, accompanying the onset of ferromagnetism and a concomitant colossal low-field magnetoimpedance (up to 80% at 600 Oe at room temperature). An oversimplified set of computations renders plausible support for interpreting these observations as arising from absorption in the spin system. Possible applications of these novel phenomena are also described.