Anomalous magnetic phase diagram of Ce(Rh1-xCox)2Ge2

We have investigated low-temperature magnetic properties of Ce(Rh1-xCox)(2)Ge-2 (0 less than or equal to x less than or equal to 1) by the measurements of the specific heat, the magnetic susceptibility and the magnetization, and obtained an anomalous magnetic phase diagram: CeRh2Ge2 exhibited two magnetic transitions at 14.5 and 8.9 K. Both transition temperatures almost linearly decrease with the Co substitution up to x similar to 0.3 and finally disappear at x similar to 0.75 following a little hump centered around x similar to 0.5. This interesting phase diagram is discussed in the framework of Doniach's model.