Pronounced quantum critical-like behavior in Ho₈Pd₅Ge₉

Materials with unconventional magnetic ground states are crucial for advancing the frontiers of fundamental physics. Here, we report the growth, structural, magnetic, electrical, and heat capacity characterization of a new quasi-1D (Q1D) compound featuring a Ho chain-like structure, namely Ho₈Pd₅Ge₉. It crystallizes in the Amm2 space group with an orthorhombic structure. It is a very good metal where the residual resistance ratio (RRR) reaches above 10³ with residual resistivity inferior to 1 μΩ cm. The material exhibits magnetic anisotropy, with evidence of an antiferromagnetic-like ordering that is visible below ~5.5 K. A broad transition is observed when the magnetic field is applied perpendicularly to the a-axis. Moreover, plateau-like features are observed in the magnetization at low temperatures as a function of applied magnetic field with a saturating value reaching 3 μ_B/Ho under a field μ₀H = 7 T. The heat capacity of the sample confirms the magnetic transition through a lambda anomaly, while displaying a gigantic increase for T < 1 K that follows a C ≅ TlnT dependence characteristic of quantum critical behavior. Given the large, localized moment of Ho, quantum critical behavior cannot be ascribed to the Doniach phase diagram inherent to heavy Fermion compounds. In addition, the A coefficient in ρ = ρ₀ + AT² where ρ is the resistivity, displays a value in the order of nΩcm/T^2, indicating a conventional metallic state. Therefore, given the quasi-one-dimensional spin chains inherent to its crystallographic structure, Ho₈Pd₅Ge₉ might provide a rare example of a metallic spin liquid.