Abstract
The effect of temperature and DC magnetic field on the microwave absorption at 9.2 GHz has been measured in as synthesized pellet samples of La 0.7Sro 0.3MnO 3 and compared with previous measurements of the temperature and DC magnetic field dependence of the bulk resistance and susceptibility in a sample of the same composition. The onset of the ferromagnetic transition at 374 K is marked by a small decrease in the surface resistance followed by a large increase below the Curie temperature in contrast to the bulk resistance which shows only a decrease. The onset of the ferromagnetic transition is also indicated by the appearance of a derivative of the absorption versus DC magnetic field centered at zero magnetic field recorded using an electron paramagnetic resonance spectrometer. The surface resistance at room temperature is much more strongly dependent on DC magnetic field strength at low DC magnetic fields decreasing by a factor of 50% for a field of 600 G. compared to only a 0.5% decrease in the resistance for the same DC magnetic field. The difference is due to the strong negative dependence of the sample permeability on DC magnetic field at room temperature. The large DC magnetic field dependence of the microwave absorption at room temperature in as synthesized samples may have potential for device applications.
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