Temperature dependence of the magnetic hyperfine field at an s-p impurity diluted in RNi₂

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We study the formation of local magnetic moments and magnetic hyperfine fields at an s-p impurity diluted in intermetallic Laves phases compounds RNi₂ (R = Nd, Sm, Gd, Tb, Dy) at finite temperatures. We start with a clean host and later the impurity is introduced. The host has two-coupled (R and Ni) sublattice Hubbard Hamiltonians but the Ni sublattice can be disregarded because its d band, being full, is magnetically ineffective. Also, the effect of the 4f electrons of R is represented by a polarization of the d band that would be produced by the 4f magnetic field.This leaves us with a lattice of effective rare earth R-ions with only d electrons. For the dd electronic interaction we use the Hubbard-Stratonovich identity in a functional integral approach in the static saddle point approximation.