Quantum criticality in the (Cr_98.4Al_1.6)_100-yMo_y alloy system

Indications of quantum critical behaviour (QCB), driven by electron-hole pair breaking effects through Mo doping of Cr_98.4Al_1.6 are reported. Previous studies on the electrical resistivity (ρ), Seebeck coefficient (S), Sommerfeld electronic specific heat coefficient (γ) and magnetic susceptibility (χ) as a function of temperature on the (Cr_98.4Al_1.6)_100-yMo_y alloy system point towards the existence of a quantum critical point (QCP) at y_c ≈ 4.5. In the present study the Hall coefficient R_H measurements and an analysis of the previous results are used to substantiate the presence of a QCP in the alloy system. The charge carrier density at 2 K, (qR_H(2K))⁻¹, of the alloy systems increases continuously with y from the antiferromagnetic (AFM) phase through y_c ≈ 4.5 and into the paramagnetic (P) phase. Scaling relationships between the magnetic contribution to the electrical resistivity, Δρ_2K, the magnetic contribution to the Sommerfeld electronic specific heat coefficient, Δγ, and (qR_H(2K))⁻¹, are furthermore used to support the presence of a QCP in the alloy system. dS/dT in the temperature limit T→ 2 K depicts an anomalous behaviour in the form of an upturn on decreasing y through the QCP, y_c ≈ 4.5. The critical exponents in the vicinity of the QCP were found to be β = 0.5 ± 0.1 for the Δρ_2K/ρ_2K(y) curve and γ = 0.4 ± 0.1 for the T_N(y) curve. The nature of the QCP in the present alloy system is classified as an incommensurate (I) spin-density-wave (SDW) type, driven mainly by electron-hole pair breaking effects.