GIANT MAGNETO RADIO-FREQUENCY ABSORPTION IN MAGNETO-RESISTIVE MATERIALS LA-0.7(SR,CA)(0.3)MNO3

The dc magnetic field, frequency, and temperature dependence of electr omagnetic absorption at rf frequencies of 335 kHz and 10 MHz are measu red in the as sintered samples of colossal magneto resistive materials La0.7Sr0.3MnO3 and La0.7Ca0.3MnO3 by measuring the penetration depth using the method of Schawlow and Devlin. Very large magneto-electromag netic absorption effects, much larger than the magneto resistive effec ts, are observed. A dc magnetic field of 1000 G changes the penetratio n depth at 350 kHz by 53% at room temperature in La0.7Sr0.3MnO3, where as the resistance of the sample only decreases by 0.75% for the same f ield. The effects are primarily a result of the decrease of the permea bility of the sample with dc magnetic field in the ferromagnetic state . A simple dc magnetometer employing the as sintered La0.7Sr0.3MnO3 co ntained in the coil of an LC oscillator as the sensing element is desc ribed.