Elucidating the lack of magnetic order in the heavy fermion CeCu₂Mg

Abstract

Magnetic, transport, and thermal properties of CeCu₂Mg are investigated to elucidate the lack of magnetic order in this heavy-fermion compound with a specific heat value, Cmag/T|T0 ≈ 1.2 J/mol K² and robust effective magnetic moments (μeff ≈ 2.46 μB). The lack of magnetic order is attributed to magnetic frustration favored by the hexagonal configuration of the Ce sublattice. In fact, the effect of magnetic field on Cmag/T and residual resistivity ρ0 does not correspond to that of a Fermi liquid (FL) because a broad anomaly appears at Tmax ≈ 1.2 K in Cmag(T)/T, without changing its position up to μoH=7.5 T. However, the flattening of Cmag/T|T0 and its magnetic susceptibility χ(T0), together with the T² dependence of ρ(T), reveal a FL behavior for T ≤ 2 K which is also supported by Wilson and Kadowaki-Woods ratios. The unusual coexistence of FL and frustration phenomena can be understood by placing paramagnetic CeCu2Mg in an intermediate section of a frustration-Kondo model. The entropy, Smag, reaches 0.87 Rln6 at T ≃ 100 K, with a tendency to approach the expected value Smag = Rln6 of the J=5/2 ground state of Ce3+.