Evolution of magnetism and superconductivity in CeCu2(Si1-xGex)(2)

Abstract

We have determined the magnetic phase diagram of CeCu2(Si1−xGex)2 using specific heat, susceptibility, and resistivity measurements and additional thermal expansion and muon spin resonance experiments. The system evolves continuously from the heavy-fermion state at x=0 to an antiferromagnetically (AF) ordered state at x=1, though the magnetic structure undergoes significant modifications. The results strongly suggest that the AF ordering emerges from the A phase of pure CeCu2Si2. The phase diagram can be divided into three regions: Low Ge content (x<~0.2) leads to an enhancement of the A phase of pure CeCu2Si2 and to a moderate decrease of the Kondo temperature. Despite this increase of the magnetic character, we could observe superconductivity up to x=0.1. At large Ge content (x>0.5) the behavior resembles that of pure CeCu2Ge2. The intermediate region is characterized by the appearance of a second magnetic transition below TN, which seems to be of first-order type. The appearance of this transition leads to a well-defined critical point at x=0.3 and suggests the possibility of another critical point at x≃0.5.