The phase diagram of CeCu2(Si1-xGex)(2)

The magnetic phase diagram of CeCu2(Si1-xGex)(2) has been studied by means of neutron diffraction to explore the transition from heavy-fermion superconductivity to local moment antiferromagnetism. This system shows up to three distinct phase transitions below 5 K. The incommensurate magnetic structure of pure CeCu2Ge2 is amazingly stable against the application of a magnetic field. With increasing Si concentration, this structure is essentially preserved down to x approximate to 0.4, where the magnetic moments are suppressed below the sensitivity of neutron powder diffraction. A further low-temperature phase transition is characterized by a spin reorientation. For x less than or equal to 0.4, a different type of magnetism is established. The nature of this new type of magnetic ordering, which may also be present in CeCu2Si2, still has to be explored. A comparison is made with the magnetic phase diagram of Ce(Cu1-xNx)(2)Ge-2.