Influence of competing energy scales on the effective spin degeneracy in CeNi9−xFexGe4

► New heavy fermion substitution series CeNi9−xFexGe4 (0 ≤ x ≤ 1). ► Remaining a four-fold degenerate ground state for x ≤ 1. ► Interplay between Kondo-effect, RKKY interaction and crystal field splitting. ► New thermodynamic macroscopic parameter: α = TR ln 4/TR ln 2. ► Kondo energy is the dominant electronic control parameter.