MAGNETIC-INTERACTIONS BETWEEN GD IONS IN GDXY1-XBA2CU3O7-DELTA - AN ESR INVESTIGATION

We analyse the ESR line width of Gd in GdxY1-xBa2Cu3O7-delta as a func tion of the Gd concentration x and temperature in the normal state. Th e powder samples were oriented in a magnetic field of 7 T. An orientat ion dependence of the line width was found. The experimentally observe d change of the ESR line width with Gd concentration x is compared wit h a model calculation based on the Gd-spin dipole-dipole and exchange interaction. The absence of resolved fine-structure splitting is expla ined by a dominance of the dipole-dipole and exchange interaction.