Schottky peaks in specific heat induced by electronic change in the antiferromagnetic-ferromagnetic alternating Kondo systemsCe(Pd1−xMx

Abstract

Kondo systems Ce͑Pd 1−x M x ͒ 2 Al 3 (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 C͑T͒ until high temperatures ͑T ഛ 150 K͒ for the above systems. A Schottky peak is observed for all the samples in the magnetic contributions to specific heat, C mag ͑T͒, 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 CePd 2 ͑Al 1−x Ga x ͒ 3 suggests that the mechanism for the FM ordering is different in the two cases.

Dramatic evolution of magnetic properties induced by electronic change in Ce(Pd1−xAgx)2Al3

“…In figure 4, we show the magnetic contribution to the specific heat, C mag , for Ce(Pd 1−x Ag x ) 2 Al 3 below 6 K. C mag is estimated by subtracting C of the La counterpart from that of the Ce one as described elsewhere [12]. Coinciding with the x dependence of χ(T ) and M(H ) curves, a similarity to Ce(Pd 1−x Cu x ) 2 Al 3 is also found in C mag .…”

“…Shown in figure 6(a) is the magnetic entropy S mag as a function of T below 15 K. S mag (T ) is obtained by numerical integration of C mag /T with respect to T , with its initial value at the lowest experimental temperature estimated by means of extrapolation. Here we limit the discussion to this low-temperature range to avoid the influence of the CEF that is observed to change with x [12]. S mag is enhanced by Ag substitution, amounting to 80% of R ln 2 (the entropy evolved by ordering temperature, S order , and the ratio Q = T K /T order as follows [13].…”

Magnetism of Ce(Pd1-xMx)2Al3(M=Ag, Cu) Based on RKKY Interaction

“…3, we plot the range of the stable ordering vectors versus x for M = ±1/2 (middle) and ±3/2 (bottom), in comparison with the experimental results [4][5][6] (top). For both M = ±1/2 and ±3/2, we theoretically obtain similar sequences of the AF order with Q = (0, 0, 1/2) for x ∼ −0.15, the F order with Q = (0, 0, 0) for x ∼ 0, and the AF order with Q = (1/2, 0, 1/2) for x ∼ 0.3.…”

“…[4][5][6] The (0, 0, 1/2)-AF order region x < 0.05 is followed by the crossover region 0.05 < x < 0.1, the ferromagnetic (F) order region 0.1 < x < 0.4, another crossover region 0.4 < x < 0.5, and another AF order (the ordering vector is unreported) region 0.5 < x. At x = 0.2, the reversed anisotropy in the susceptibility of χ a /χ c < 1 is observed, 4,5) indicating that the CEF ground state has changed from the M = ±1/2 states to other states. We assume the CEF ground state for the doped system as M = ±3/2, because the estimated splitting from the ground state M = ±1/2 is small in the undoped system (CePd 2 Al 3 ).…”

Simultaneously optimizing the interdependent thermoelectric parameters in Ce(Ni$_{1-x}$Cu$_x$)$_2$Al$_3$

“…The evolution of ρ in the reference system hints that the decrease of ρ with x in Ce(Ni 1−x Cu x ) 2 Al 3 shares the same origin: it is due to a decrease of the usual electron-phonon scattering term ρ p , assuming that ρ = ρ 0 +ρ p +ρ m , where ρ 0 is the residual resistivity and ρ m the magnetic part occurring only in the Ce compounds. On the other hand, γ diminishes with x in La(Pd 1−x Ag x ) 2 Al 3 [15], indicative that the full-filled d-band of Cu triggers a shift of the Fermi level away from the enhanced DOS of d character. Similar effect is confirmed both experimentally and theoretically in Ce(Pd 1−x Cu x ) 2 Si 2 [16].…”