Magneto-impedance measurements in bulk samples of La0.7Ca0.3MnO3 and La0.6Y0.1Ca0.3MnO3

In this work, magneto-resistance and magneto-impedance (MI) data for bulk samples of pure and Y-doped La0.7Ca0.3MnO3 manganites are reported. Temperature dependent measurements were carried out sweeping the applied magnetic field H in the -6 T < H < 6 T range. The measurements were done with do and ac electrical currents, varying the frequencies f up to 5 MHz, using a four-probe technique. The pure La0.7Ca0.3MnO3 sample presented a metal-insulator-transition near the ferromagnetic transition (T-C = 245 K). For these samples, magneto-resistance of the order 60% for H = 6 T was observed close to T-C. The substitution of ions of La by Y (La0.6Y0.1Ca0.3MnO3) reduced T-C to 170 K but, on the other hand, increased the magneto-resistance to over 90% near T-C. In the measurements with ac currents, the data for both samples presented a large magneto-impedance effect. The MI is more pronounced at high fields and for the Y-doped samples. Moreover, the Y-doped samples showed a strong hysteretic behavior that was not observed in the pure samples. (C) 2003 Elsevier B.V. All rights reserved.