High pressure Moessbauer studies on Yb heavy fermion compounds

The discovery that some Yb intermetallic compounds exhibit many of the interesting Kondo-related properties found in analogous Ce compounds has led to a number of new experimental and theoretical activities to understand the ground state properties of this class of materials. In this paper we give a brief review of our very recent results on the effect of pressure on the magnetic and electronic properties of the ferromagnetic Kondo lattice (KL) YbNiSn and isostructural antiferromagnetic KL YbPtAl using the 170Yb Moessbauer effect technique, electrical resistance and X-ray diffraction, respectively. We show that the magnetic ground state properties of YbNiSn and YbPtAl are governed by a volume dependent competition between frustrated anisotropic exchange interactions and the crystal electric field anisotropy rather than by a direct competition between Kondo and RKKY interactions