Itinerant to local transformation and critical point in Ni-rich Ce₂(Ni_1-yPd_y)₂Sn alloys

Abstract

Structural, magnetic (M ) and thermal (Cm) studies on Ce2(Ni1−yPdy)2Sn alloys are presented within the 0 ≤ y ≤ 0.55 range of concentration, showing evidences for itinerant to local electronic transformation. At variance with RKKY type interactions between localized moments µ ef f , the substitution of Ni by isoelectronic Pd leads the antiferromagnetic transition to decrease from TN 3.8 K to 1.2 K between y = 0 and 0.48, while M (H) measured at H = 5 T and 1.8 K rises from 0.12 up to 0.75µB/Ce-at. Furthermore, the Cm(TN ) jump increases with concentration whereas |θP | decreases. The magnetic entropy Sm(T ) grows moderately with temperature for y = 0 due to a significant contribution of excited levels at low energy, while at y = 0.5 it shows a incipient plateau around Sm = Rln2. All these features reflect the progressive ground state transformation of from itinerant to a local character.Another peculiarity of this system is the nearly constant value of Cm(TN ) that ends in an entropy bottleneck as TN decreases. Consequently, the system shows a critical point at ycr ≈ 0.48 with signs of ferromagnetic behavior above Hcr ≈ 0.3T. A splitting of the Cm(TN ) maximum, tuned by field and concentration, indicates a competition between two magnetic phases, with respective peaks at TN ≈ 1.2 K and TI ≈ 1.45 K.