MAGNETIC INSTABILITIES IN CE COMPOUNDS - EFFECT OF PRESSURE AND CHEMICAL SUBSTITUTIONS

Many intermetallic Ce compounds have magnetic ground states unstable under pressure and vs anion concentration in alloys. We analyze the magnetic instability by calculating the magnetic moment in the local spin density approximation and the hybridization width Δ of the Anderson model as a function of volume reduction and composition in CeCd1-xZnx, CeAg1-xZnx, and CeCd1-xAgx. For x=0, Δ is found to increase with volume reduction, as expected. Our calculations may thus explain the behavior of TC vs pressure observed in CeAg in terms of the RKKY-Kondo competition driven by the increase of the s-f coupling. In the case of ternary solid solutions, the behavior of Δ vs volume contraction is opposite to that expected from electronic pressure considerations in CeAg1-xZnx and CeCd1-xZnx, pointing to the predominance of electronic effects in alloys. This may explain the behavior of the magnetic moment and transition temperature observed in the latter compound and qualitatively in Ce(Rh1-xRux)Si2 and U(Rh1-xRux)Si2. We carry out calculations of Δ and of the magnetic moment vs pressure also for GdAg, which is a ferromagnet with stable f moments. The comparison with its Ce counterpart underlines the different behavior of the f electrons to determine the magnetic stability of the two compounds.