From itinerant to local transformation and critical point in Ni-rich Ce_2(Ni_{1-y}Pd_y)_2Sn

Abstract

Structural, magnetic (M) and thermal (C_m) studies on Ce_2(Ni_{1-y}Pd_y)_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 \mu_{eff}, the substitution of Ni by isoelectronic Pd leads the antiferromagnetic transition to decrease from T_N~3.8K to ~1.2K between y=0 and 0.48, while M(H) measured at H=5Tesla and 1.8K rises from 0.12 up to 0.75\mu_B/Ce-at. Furthermore, the C_m(T_N) jump increases with concentration whereas |\theta_P| decreases. The magnetic entropy S_m(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 S_m=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 C_m(T_N) that ends in an "entropy bottleneck" as T_N decreases. Consequently, the system shows a critical point at y_{cr}~0.48 with signs of ferromagnetic behavior above H_{cr}~0.3T. A splitting of the C_m(T_N) maximum, tuned by field and concentration, indicates a competition between two magnetic phases, with respective peaks at T_N~1.2K and T_I~1.45K.