Competition between ferromagnetism and frustrated antiferromagnetism in quasi 2D Ce2.15(Pd1-x Ag x )1.95In0.9 alloys.

Low temperature thermal and magnetic measurements performed on ferro-magneticl (FM) alloys of composition Ce2.15(Pd1-x Ag x )1.95In0.9 are presented. Pd substitution by Ag depresses [Formula: see text] from 4.1 K down to 1.1 K for x  =  0.5, which is related to the increase of band electrons, with a critical concentration extrapolated to [Formula: see text]. The [Formula: see text] decrease is accompanied by a weakening of the magnetization of the FM phase. At high temperature (T  >  30 K) the inverse magnetic susceptibility reveals the presence of robust magnetic moments ([Formula: see text] [Formula: see text]), whereas the low value of the Curie-Weiss temperature [Formula: see text] K excludes any relevant effect from Kondo screening. The specific heat jump at [Formula: see text] decreases accordingly, while an anomaly emerges at a fixed temperature [Formula: see text] K. This unexpected anomaly does not show any associated sign of magnetism checked by AC-susceptibility measurements. Since the total magnetic entropy (evaluated around [Formula: see text]) practically does not change with Ag concentration, the transference of degrees of freedom from the FM component to the non-magnetic T (*) anomaly is deduced. The origin of this anomaly is attributed to an arising magnetic frustration of the ground state and the consequent entropy bottleneck produced by the divergent increasing of density of excitations at low temperature.