ESR IN THE Y1-XGDXBA2CU3O7 SYSTEM BELOW T(C)

The ESR spectra from GdBa2Cu3O7 between 300 and 10 K are presented and shortly discussed. Below Tc, the signal from sintered samples is lost (X band) or weak (Q band). The ESR line from single crystals, while D ysonian and isotropic at 300 K, is symmetrical and significantly aniso tropic below 40 K, and presents then an additional narrowing when H // ab. In the dilute compounds (x less than or similar to .02) an experi mental answer is given to a question raised at LT19, to be solved befo re low T studies.