GIANT MAGNETORESISTANCE AT MICROWAVE-FREQUENCIES

We report the first measurement of giant magnetoresistance at 10 GHz i n a bulk ceramic sample of Nd0.7Sr0.3MnO3. From the surface resistance data, we deduce that the magnetoresistance, [rho(mu W)(0) - rho(mu W) (B)]/rho(mu W)(0) at 1.2 T, has a peak value of approximately 90% at 2 15 K. The microwave studies are supplemented by data on low-field (les s than or equal to 3.5 mT) d.c. magnetization and d.c. resistivity. Fr om the magnetization data, we find that T-c = (219 +/- 2) K. The zero- field microwave loss peaks at T-p = (216 +/- 2) K. The field dependenc e of the microwave absorption suggests that these materials can prove to be extremely useful in designing microwave devices.