MAGNETIC-SUSCEPTIBILITY STUDIES IN GD2CUO4 BELOW 300-K

Measurements of the real (X') part of the ac magnetic susceptibility h ave been performed on two polycrystalline Gd2CuO4 samples sintered at different temperatures, 850 degrees C and 1080 degrees C in the temper ature range 10<T(K)<300. Two well-defined maxima have been observed in the temperature dependence of X'. One, located at about 20 K, that is frequency independent. The second is at about 280 K for the sample an nealed at 1080 degrees C, and it is frequency independent. Instead, fo r the sample annealed at 850 degrees C the maximum appears at about 21 0 K, and it is frequency dependent. These results suggest the existenc e of magnetic domains, with their coherence lengths being a function o f the thermal treatment.