Chemical tuning and suppression of AFM order in the corrugated kagome metal La₂(Co_1-xNi_x)₃

Geometrically frustrated crystal structures, such as the kagome or pyrochlore networks, have long been recognized as fruitful platforms for hosting emergent physical phenomena. It is only recently appreciated that when metals adopt such structures, destructive quantum interference of electron hopping paths enforces real-space electronic localization and associated flat bands in reciprocal space. These flat bands are topologically non-trivial in nature and produce high densities of states that may favor magnetic, superconducting, or other instabilities, motivating identification and study of families of metallic compounds with geometrically frustrated crystal structures. Here, we provide a detailed study of La₂Co₃, La₂Ni₃, and the series La₂(Co_1-xNi_x)₃, in which the transition metal atoms adopt buckled kagome sheets. Both density functional theory and preliminary ARPES measurements suggest the presence of extremely flat, Co 3d-orbital based bands near the Fermi level in La₂Co₃ that can be continuously tuned away from E_F by electron doping (Ni substitution). We find that La₂Co₃ orders antiferromagnetically at T_N ~ 310 K, and that Ni substitution monotonically suppresses AFM ordering such that long-range order vanishes above x ~ 0.46. Notably, at Ni fractions close to the suppression/onset of magnetic order, we observe both an enhanced electronic specific heat coefficient and deviation from the expected resistive behavior, with the resistance developing an anomalous low temperature upturn. These factors indicate that a quantum critical point may occur near x ~ 0.46 in La₂(Co_1-xNi_x)₃. We conclude by comparing our results to recent work exploring suppressed magnetic order in kagome metals and discuss open questions and opportunities for future research.