Magnetic hyperfine field at a Cd impurity diluted in RCo2 at finite temperatures

The local magnetic moments and the magnetic hyperfine fields at an s-p Cd impurity diluted in inter-metallic Laves phase compounds RCo2 (R=Gd, Tb) at finite temperatures are calculated. For other rare earth elements (light or heavy) the pure compounds display a magnetic first order transition and are not describable by our formalism. The host has two coupled lattices (R and Co) both having itinerant d electrons but only the rare earth lattice has localized f electrons. They all contribute to the magnetization of the host and also to the local moment and to the magnetic hyperfine field at the impurity. The investigation of magnetic hyperfine field in these materials then provides valuable information on the d-itinerant electrons and also on the localized (4f) magnetic moments. For the d-d electronic interaction we use the Hubbard-Stratonovich identity thus allowing the employment of functional integral in the static saddle point approximation. Our model reproduces quite well the experimental data.