Magnetic and related properties of Ce5CoGe2, CeCoGe and CeCo2Ge2

• Physical properties of Ce5CoGe2 were studied for the first time.
• Physical properties of CeCoGe and CeCo2Ge2 were reinvestigated.
• Ce5CoGe2 is ferromagnetically ordered below about 11 K.
• Thermoelectric power of the three phases was studied for the first time.
• Thermoelectric power of Ce5CoGe2 is distinctly larger than in CeCoGe and CeCo2Ge2.

Magnetic susceptibility, magnetization, specific heat, electrical resistivity and thermoelectric power of polycrystalline Ce5CoGe2, CeCoGe and CeCo2Ge2 were studied at temperatures down to 2 K and in magnetic fields up to 5 T. The novel phase Ce5CoGe2 was found to be a ferromagnet with the Curie temperature of about 11 K, which exhibits in the paramagnetic region some features of a dense Kondo system with strong crystal field effect. The re-investigated CeCoGe was found to order antiferromagnetically below 4.6 K, while CeCo2Ge2 is an intermediate-valence system, in agreement with previous reports. The thermoelectric power of the latter compound is large (up to 40 μV/K) and positive in the whole temperature range studied, while in the magnetically ordered systems Ce5CoGe2 and CeCoGe it is mostly negative and distinctly smaller (down to −1.5 and −11 μV/K, respectively).