Crossover from First-Order Valence Transition to Kondo Behavior in C15b-Type YbCu_5-xIn_x System

Abstract

YbCu₅ and YbCu₄In forms a solid-solution (YbCu_5-xIn_x) with cubic AuBe₅-type (C15b) structure in the In-concentration range 0.1≤ x≤ 1; and below x=0.1, it coexists with a hexagonal CaCu₅-type YbCu₅ phase under ambient pressure. The magnetic susceptibility and high-field magnetization measurements reveal that the first-order valence transition in YbCu₄In shifts to higher temperature and becomes broadened significantly with decreasing In-content, and simultaneously the delocalized mixed-valent state of Yb ion (x=1) shows a continuous change toward the localized trivalent state (x=0). The electrical resistivities of YbCu_5-xIn_x display various temperature-dependencies: ranging from a pronounced drop at x=1, via a minimum behavior for 0.4≤ x≤ 0.7, to a negative logarithmic increasing behavior (-ln T) for x≤ 0.3. Above results suggest that YbCu_5-xIn_x goes through a crossover from a valence fluctuation system to a dence Kondo one with decreasing x. At x=0, the formation of Kondo lattice is predicted.