High-energy paramagnetic spectral response of the valence fluctuation compound YbAl₂

Abstract

Measurements of the paramagnetic spectral response of YbAl₂, reveal a broad Lorentzian inelastic hump closely similar to that of α-Ce in spectral shape, in integrated intensity (within ± 20% uncertainty), as well as in characteristic energy ω _o (=180 ± 10meV). Relating the latter to the linear specific heat coefficient y via a Fermi-liquid relation requires that the 4f occupancy (n _f) be close to unity (i.e. 0.9 ± 0.1). With the same values of (n _f) and ω _o the Fermi-liquid relation for the low-temperature bulk susceptibility χ(0) yields a reduced effective moment of magnitude close to that for the crystal-field Γ₇, state (N = 2) or the J = 5/2; spin-orbit state (N = 6), the latter implying an inversion of Hund's rule states of Yb. The nearly integral valence of Yb in YbAl₂, suggested by the Fermi-liquid analysis is in conflict with the lattice constant, photoemission and L₁₁₁ X-ray absorption data which all yield (n _f)≈ 0·4.