FRUSTRATION IN ITINERANT ANTIFERROMAGNETS

Frustration is present in most antiferromagnetic compounds, either due to the lattice structure or to the existence of competing long-range interactions. We show that, close to a magnetic-nonmagnetic instabilit y, frustration can lead to the stabilization of phases where both magn etic and nonmagnetic sites are present. Several examples are discussed : the RMn2 compounds where the Mn 3d magnetic moment is unstable; CeSb and UNi4B in which the Kondo effect can be responsible for the instab ility. We present a model which includes both ingredients: frustration and magnetic instability, and explain qualitatively the unusual magne tic structures observed in these compounds.