Competing magnetic interactions in CeNi_9−xCo_xGe₄

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

“…For CeNi 8.8 Fe 0.2 Ge 4 the upper maximum increases and remains at the same temperature while the Kondo-type anomaly decreases as it is also observed in the homologous CeNi 8.8 T 0.2 Ge 4 (T: Co, Cu) [12,13]. This common behavior at lowest level of substitution is most likely a consequence of disorder introduced in the pseudo-ternary solid solution.…”

“…1 the concentration dependence of the tetragonal lattice parameters a = b and c follows Vegard's law for both solid solutions CeNi 9−x Fe x Ge 4 and LaNi 9−x Fe x Ge 4 . This observation is different to the Co substitution series where no significant volume change was observed in the stoichiometric range of 0 ≤ x ≤ 1 [13]. On contrast, the clear change of chemical pressure in the CeNi 9−x Fe x Ge 4 series upon Ni by Fe substitution should significantly influence the hierarchy of competing Kondo, RKKY and CF interactions and help to identify the control parameter for the onset of AF ordering at low temperatures.…”

“…3b), where an antiferromagnetic transition sets in for x≥ 0.4 [13]. The observation of magnetic order in CeNi 9−x Co x Ge 4 is surprising because a reduction of the 3d electron count, accompanied with an increase of the N(E F ) (see Fig.…”

“…Indeed, no magnetic order is observed in CeNi 9 Ge 4 down to the lowest experimentally reached temperatures (35 mK). Subsequent substitution of Ni by the neighboring transition metals, Cu and Co, causes in both cases a reduction of the effectively four-fold degeneracy of the Kondo ground state toward an effectively two-fold one and long range antiferromagnetic (AF) order is observed with T N = 0.2 K and 1 K for CeNi 8 CuGe 4 and CeNi 8 CoGe 4 , respectively [12,13]. In case of Cu doping a tendency toward AF order is indeed expected due to an increase of the 3d-electron count.…”

“…6. The entropy temperature ratio ˛ = T R ln 4 /T R ln 2 with respect to the Fe, Co [13] and Cu [12] amount x.…”