Evolution from first-order valence transition to heavy-fermion behavior inYbIn1−x

J. L. Sarrao

¹

,

C. D. Immer

²

,

C. L. Benton

³

et al.

Abstract

YbInCu 4 undergoes a first-order isostructural valence transition near 40 K, whereas YbAgCu 4 is a moderately heavy ͑␥ϭ250 mJ/mol K 2 ͒ mixed-valence compound. We have succeeded in growing single crystals of these compounds, as well as many intermediate alloys, using flux-growth techniques. The evolution from YbInCu 4 to YbAgCu 4 has been characterized using electrical resistivity, magnetic susceptibility, and x-ray powder diffraction. The data are interpreted in terms of the evolution of the single-impurity Kondo temperature as a function

Ultrasonic study of the mixed-valence systemYbIn1−xAgxCu<

“…8 The typical size of the samples used in our ultrasonic experiments was 1.2ϫ1.5ϫ1.5 mm 3 . We utilized transverse resonant quartz transducers with a fundamental frequency of 10 MHz and piezoelectric films in case of longitudinal sound excitation.…”

“…The magnetic susceptibility drops suddenly at the phase transition and shows nearly temperature-independent Pauli-like paramagnetic behavior at low temperatures. 1,8 So far no magnetic order has been found in YbInCu 4 at low temperatures. 1 The…”

“…It turns out that the phase transition involves a large change of the Kondo temperature from T K ϳ20 K in the hightemperature phase to T K ϳ430 K at low temperatures. 8 Earlier ultrasonic investigation 3,4 revealed a strong softening of the bulk modulus c B of 43% at the transition temperature and a change of the Poisson ratio of 30%. At the same time transverse-acoustic modes demonstrated steplike anomalies in the sound velocity that was not typical for an isostructural phase transition.…”

“…1,[3][4][5][6][7] The phase transition takes place at a critical temperature of T v Х40 K, although some crystals showed the phase transition at temperatures up to 66 K. 3 Silver doping moves the transition to higher temperatures and makes it to be of second order. 6,8 Pure YbAgCu 4 appears to be a moderately heavy fermion (␥ ϭ250 mJ/mol K 2 ) compound. 8,9 YbInCu 4 has a facecentered-cubic C15b structure and the valence phase transition is accompanied by the abrupt increase in the lattice parameter by about 0.13% without any change in the space symmetry.…”

“…6,8 Pure YbAgCu 4 appears to be a moderately heavy fermion (␥ ϭ250 mJ/mol K 2 ) compound. 8,9 YbInCu 4 has a facecentered-cubic C15b structure and the valence phase transition is accompanied by the abrupt increase in the lattice parameter by about 0.13% without any change in the space symmetry. 10,11 The cell volume was found to vary proportionally to n f .…”