Evolution of thermopower across a quantum-critical point: The (Cr₈₆Ru₁₄)_1-xV_x system

Thermopower (S) and electrical resistivity (ρ) measurements are reported for a polycrystalline (Cr₈₆Ru₁₄)_1-xV_x alloy system, with 0 ≤ x ≤ 0.144. The results reveal peculiar transport properties not observed in other Cr alloy systems. This study focusses on S(T) of these alloys as a parameter that is sensitive to changes in the electronic structure and scattering mechanisms of importance at the spin-density-wave Néel transition. Of significance is the deep minima observed in S(T) for alloys with x ≤ 0.045, well below the critical concentration x _c, at T < T _N. These are attributed to a possible negative component of magnetic origin combined with phonon drag effects, due to the Ru diluent in these alloys. This is suggested to compete with the decrease in the scattering rate of electrons by phonons below TN as the V concentration is increased and a dome is observed in S(T) for alloys close to x _c, with 0.074 ≤ x ≤ 0.101. The temperature - composition magnetic phase diagram obtained from the S(T) and ρ(T) measurements depicts a critical point, occurring at T = 0 K for a critical V concentration x _c = 0.106. The Nordheim-Gorter relationship is obeyed in the concentration range 0.032 ≤ x ≤ 0.111.