Elucidating the lack of magnetic order in the heavy-fermion CeCu₂Mg

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, C_mag/T |_T→0 ≈ 1.2 J/mol K² and robust effective magnetic moments (μ_eff ≈ 2.46μ_B). 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 C_mag/T and residual resistivity ρ₀ does not correspond to that of a Fermi liquid (FL) because a broad anomaly appears at T_max ≈ 1.2 K in C_mag(T )/T , without changing its position up to μ₀H = 7.5 T. However, the flattening of C_mag/T |_T→0 and its magnetic susceptibility χ_T→0, 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, S_mag, reaches 0.87 R ln 6 at T _ 100 K, with a tendency to approach the expected value S_mag = R ln 6 of the J = 5/2 ground state of Ce³⁺.