Ferromagnetic instability at the edge of intermediate valence

Abstract Preliminary study of structural, thermal and magnetic properties on ferromagnetic CePt 1 - y Rh y ( 0.40 ⩽ y ⩽ 1 ) is presented. Like in the recently studied CePd 1 - x Rh x , this new system undergoes a quantum critical behavior between the ferromagnetic CePt ( T C = 6 K ) and unstable valence CeRh. Regardless the electronic and atomic size similarities between Pt and Pd atoms, significant differences in their respective phase diagrams are observed around the critical points. While CePd 1 - x Rh x shows an asymptopic T C ( x ) decrease indicating a smeared quantum phase transition, in CePt 1 - y Rh y T C ( y ) vanishes beyond y = 0.80 after a plateau starting at y = 0.60 at T C ≈ 1.8 K . Peculiarities of this critical region are compared with other Ce-systems.