Themal Expansion and Magnetostriction of YbAuCu₄

Precise thermal expansion and magnetostriction measurements were performed on the heavyfermion compound YbAuCu₄ in order to examine the crossover valence transition at T_V which was proposed by the nuclear magnetic resonance measurements. The temperature dependence of the thermal expansion coefficient α under magnetic fields shows a broad peak, which shifts to higher temperatures with increasing magnetic fields. The corresponding linear thermal expansion Δℓ/ℓ parallel to the magnetic field of 7.0 T shows a marked decrease below about 10 K, indicating a contraction of sample length at low temperatures. These results are discussed in relation to the observed temperature dependence of the nuclear quadrupole frequency ν_Q under magnetic fields.