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要旨

We report on single-crystal growth and physical properties of the quantum critical Kondo-lattice system YbNi4(P1-xAsx)2 with 0≤x≤1 which hosts a ferromagnetic quantum critical point at x≈0.1. We performed measurements of the magnetization, electrical resistivity, thermopower, heat capacity, and resonant x-ray emission spectroscopy. Arsenic substitution leads to a homogeneous increase of the unit-cell volume, with well-defined As concentrations in large parts of the single crystals. All data consistently show that with increasing x the Kondo temperature increases, while the magnetic anisotropy observed at low x fully vanishes toward x=1. Consequently, at low temperatures, the system shows a crossover from pronounced non-Fermi liquid behavior for x≤0.2 to a Fermi liquid behavior for x>0.2 with weak correlations. There is a continuous change in Yb valence from nearly trivalent at low x to a slightly lower value for x=0.6, which correlates with the Kondo temperature. Interestingly, specific heat measurements at very low temperatures show that C/T strongly increases toward lower T for x=0.13 and x=0.2 with a very similar power law. This suggests that in YbNi4(P1-xAsx)2 a quantum critical line rather than a quantum critical point might exist. © 2025 American Physical Society.