Emerging frustration effects in ferromagnetic Ce_2[Pd_{1-x}Ag_x]_2In alloys

TL;DR

This study investigates how substituting Pd with Ag in Ce-based ferromagnetic alloys affects their magnetic properties, revealing a quantum critical point and unusual entropy behavior near 1K.

Contribution

It identifies a quantum critical point at x~0.6 and uncovers a novel entropy bottleneck phenomenon in ferromagnetic Ce alloys with Ag substitution.

Findings

Quantum critical point at x~0.6 where T_C approaches zero

Emergence of a specific heat anomaly at ~1K

Magnetic entropy remains nearly constant around 4K

Abstract

Magnetic and thermal properties of Ferromagnetic (FM) Ce_{2.15}(Pd_{1-x}Ag_x)_{1.95}In_{0.9} alloys were studied in order to determine the Quantum Critical Point (QCP) at T_C => 0. The increase of band electrons produced by Pd/Ag substitution depresses T_C(x) from 4.1K down to T_C(x=0.5)=1.1K, with a QCP extrapolated to x_{QCP}~ 0.6. Magnetic susceptibility from T>30K indicates an effective moment slightly decreasing from \mu_{eff}=2.56\mu_B to 2.4\mu_B at x=0.5. These values and the paramagnetic temperature \theta_P~ -10K exclude significant Kondo screening effects. The T_C(x) reduction is accompanied by a weakening of the FM magnetization and the emergence of a specific heat C_m(T) anomaly at T*~ 1K, without signs of magnetism detected from AC-susceptibility. The magnetic entropy collected around 4K (i.e. the T_C of the x=0 sample) practically does not change with Ag concentration: S_m(4K)~ 0.8 Rln2, suggesting a progressive transfer of FM degrees of freedom to the non-magnetic (NM) component. No antecedent was found concerning any NM anomaly emerging from a FM system at such temperature. The origin of this anomaly is attributed to an 'entropy bottleneck' originated in the nearly divergent power law dependence for T>T*.