Quantum phase transitions and multicriticality in Ta(Fe_1-xV_x)₂

We present a comprehensive study of synthesis, structure analysis, transport and thermodynamic properties of the C14 Laves phase Ta(Fe_1-xV_x)₂. Our measurements confirm the appearance of spin-density wave (SDW) order within a dome-like region of the x-T phase diagram with vanadium content 0.02 < x < 0.3. Our results indicate that on approaching TaFe₂ from the vanadium-rich side, ferromagnetic (FM) correlations increase faster than the antiferromagnetic (AFM) ones. This results in an exchange-enhanced susceptibility and in the suppression of the SDW transition temperature for x < 0.13 forming the dome-like shape of the phase diagram. This effect is strictly related to a significant lattice distortion of the crystal structure manifested in the c / a ratio. At x = 0.02 both FM and AFM energy scales have similar strength and the system remains paramagnetic down to 2 K with an extremely large Stoner enhancement factor of about 400. Here, spin fluctuations dominate the temperature dependence of the resistivity ρ ∝ T^3/2 and of the specific heat C/T ∝-log(T) which deviate from their conventional Fermi liquid forms, inferring the presence of a quantum critical point of dual nature.