Investigation of the physical properties of the Ce2MAl7Ge4 (M = Co, Ir, Ni, Pd) heavy fermion compounds

We report the synthesis, crystal structure and characterization by means of single crystal x-ray diffraction, neutron powder diffraction, magnetic, thermal and transport measurements of the new heavy fermion compounds Ce\(_{2}\)MAl\(_{7}\)Ge\(_{4}\) (M = Co, Ir, Ni, Pd). These compounds crystallize in a noncentrosymmetic tetragonal space group P\={4}2\(_{1}\)m, consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce\(_{2}\)CoAl\(_{7}\)Ge\(_{4}\), Ce\(_{2}\)IrAl\(_{7}\)Ge\(_{4}\) and Ce\(_{2}\)NiAl\(_{7}\)Ge\(_{4}\) order magnetically behavior below \(T_{M}=\) 1.8, 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce\(_{2}\)PdAl\(_{7}\)Ge\(_{4}\) down to 0.4 K. The small amount of entropy released in the magnetic state of Ce\(_{2}\)MAl\(_{7}\)Ge\(_{4}\) (M = Co, Ir, Ni) and the reduced specific heat jump at \(T_M\) suggest a strong Kondo interaction in these materials. Ce\(_{2}\)PdAl\(_{7}\)Ge\(_{4}\) shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point.