Magnetic phase diagram of CeAu2Ge2

CeAu2Ge2 single crystals (tetragonal ThCr2Si2 structure) have been grown in Au-Ge flux (AGF) as well as in Sn flux (SF). X-ray powder diffraction measurements and EDX measurements indicate that in the latter case Sn atoms from the flux are incorporated in the samples, leading to a decrease of the lattice constants by ∼0.3 % compared to AGF samples. The magnetization M demonstrates a strong dependence of the magnetic properties on the flux employed. While the SF samples adopt simple antiferromagnetic order below 9 K, a sequence of metamagnetic transitions with increasing magnetic field in the AGF samples points towards a more complex magnetic structure for B parallel c. One the basis of the neutron scattering data of Loidl et al. (PRB 46, 9341, 1992) we calculated the field-dependence of the magnetization at T=20 K in the paramagnetic regime, as well as the temperature dependence, and found good agreement with our measured data for B parallel c and B perpendicular to c. The complex phase diagram of the AGF samples in comparison to the simpler one of the SF samples is discussed within the framework of the ANNNI model, making CeAu2Ge2 a possible candidate for a Devil's Staircase.