Quantum critical point followed by Kondo-like behavior due to Cu substitution in itinerant, antiferromagnet La2(CuxNi1−x)7

Abstract

La2Ni7 is an itinerant magnet with a small saturated moment of ∼ 0.1 μB/Ni and a series of antiferromagnetic (AFM) transitions at T1 = 61.0 K, T2 = 56.5 K and T3 = 42.2 K. Temperature and field dependent measurements suggest a complex, anisotropic H−T phase diagram with multiple phase lines. Here we present the growth and characterization of single crystals of the La2(CuxNi1−x)7 series for 0 ≤x≤ 0.181. Using a suite of anisotropic magnetic, transport, and thermodynamic measurements we study the evolution of the three AFM transitions upon Cu substitution. For 0≤x≤0.097, the system remains magnetically ordered at base temperature with x≤ 0.012, showing signs of three primarily AFM phases. For the higher substitution levels, 0.125≤x≤0.181, there are no signatures of magnetic ordering, but an anomalous feature in resistance and heat capacity data are observed which are consistent with the Kondo effect in this system. The intermediate x = 0.105 sample lies in between the magnetic ordered and the Kondo regime and is in the vicinity of the AFM-quantum critical point (QCP). Thus, La2(CuxNi1−x)7 is an example of a small moment system that can be tuned through a QCP. Given these data combined with the fact that the La2Ni7 structure has kagome-like, Ni-sublattice running perpendicular to the crystallographic c− axis, and a 3d-electron flat band that contributes to the density of states near the Fermi energy, it becomes a promising candidate to host and study exotic physics.