Coupled spin-lattice transition in: Thermal expansions and magnetization

Abstract

We have measured the thermal expansion, (Formula presented) and high-field magnetization, (Formula presented) along the three quasiorthorhombic axes of (Formula presented). There are discontinuities in (Formula presented) at (Formula presented) = 25.7 K of opposite sign in the (Formula presented) and (Formula presented) directions while the (Formula presented) axis changes steplike, which tracks a large volume change. The magnetization along the (Formula presented) axis, (Formula presented), exhibits a dramatic temperature-dependent metamagnetic transition where the induced U moments switch from 0.1 to 1.7(Formula presented) while the (Formula presented) and (Formula presented) axes remain unperturbed. We relate these anomalies to a first-order phase transition of strongly coupled spin and quadrupole orderings. © 1997 The American Physical Society.