Schottky peaks in specific heat induced by electronic change in the antiferromagnetic-ferromagnetic alternating Kondo systems Ce(Pd _1-xM_x)₂Al₃ (M=Cu or Ag)

Kondo systems Ce(Pd_1-xM_x)₂Al₃ (M=Cu or Ag) have been previously shown to display antiferromagnetic (AFM) or ferromagnetic (FM) ordering alternatively then produce a complex phase diagram of AFM-FM-AFM type depending on the substitution amount x. This paper reports the results of specific heat C(T) until high temperatures (T≤ 150 K) for the above systems. A Schottky peak is observed for all the samples in the magnetic contributions to specific heat, C_mag(T), while deviating from a typical one on substitution. Unusual Schottky peaks that spread over a very wide temperature range with considerably small values can be confirmed at least around x=0.2-0.3 where FM ordering just occurs. The unusual Schottky peaks are phenomenologically associated with randomness in the crystal electric field induced by the Pd-M replacements, and the randomness is discussed as a probable origin of the AFM-FM transition. In addition, a comparison between the present systems and the relevant AFM-FM transition system CePd₂(Al _1-xGa_x)₃ suggests that the mechanism for the FM ordering is different in the two cases.