  Neutron diffraction measurements on a high quality single crystal of CeAu2Ge2
reveal two new magnetic structures that coexist with commensurate long range
antiferromagnetic order below the Neel temperature T_N ~ 14 K. The new magnetic
structures, which exhibit distinct temperature and field dependencies, are
described by both commensurate and incommensurate magnetic structures and
introduces new region in the H-T phase diagram. These new experimental
observations provide essential information for developing a universal
understanding of the magnetic properties of this class of Ce-based CeX2M2 (X =
Cu, Ag, Au; M = Ge, Si) compounds, which are prototypes for exploring quantum
phase transitions and their interplay with unconventional superconductivity.
