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 function of the Gd concentration x and temperature in the normal state. The powder samples were oriented in a magnetic field of 7 T. An orientation dependence of the line width was found. The experimentally observed change of the ESR line width with Gd concentration x is compared with a model calculation based on the Gd-spin dipole-dipole and exchange interaction. The absence of resolved fine-structure splitting is explained by a dominance of the dipole-dipole and exchange interaction.