Estudo da MagnetoimpedÃncia em La0;7Ca0;3MnO3 e La0;6Y0;1Ca0;3MnO3




In the present work, we report high frequency lock-in detection tecniques. The techniques were used to investigate La0:7Ca0:3MnO3 and La0:6Y0:1Ca0:3MnO3 manganites. The measurements were carried out at temperatures ranging from 50 to 300 K, and for applied magnetic fields up to 6 T, using both dc and ac currents. The frequency f of the ac current was varried from 100 kHz to 3.0 MHz. The metal- insulator transition temperatures obtained were 260 and 167.5 K and the maxima magnetoresitance (MR) were 83% and 91% for the samples with and without Y, respectively. The ac data allowed us to investigate both the real and the out-of-phase components. For temperatures far from TP , the impedance is mostly resistive while the out-of-phase component becomes signficantly larger near Tp. The real component of impedance shows a double peak structure for high frequencies. This effect is more evident for the sample with Y. Near Tp we also found that the magnetoimpedance is maximum for the sample without Y, while for the other one the maximum is bellow TP and shows strong f-dependence. The low-field data show a hysteresis only in the La0:6Y0:1Ca0:3MnO3 sample suggesting that Y induce a random anisotropy


fisica 1ca0 3mno3 - magnetoimpedÃncia 6y0 la0 3mno3 e la0 7ca0

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