Spin dynamics and magnetic ordering in mixed valence systems

Abstract

Neutron scattering measurements are reported on the mixed valence compounds Ce_1−xTh_x and TmSe. The χ^″ (Q,ω) as derived from the inelastic spectra of Ce_0.74Th_0.26 shows a peak in the γ phase near 20.0 meV and shifts abruptly to greater than 70.0 meV at the transition to the α phase. The temperature independence of the susceptibility within the γ phase cannot be simply reconciled with the temperature dependence of the valence within the γ phase. TmSe is shown to order in a type I antiferromagnetic structure below T_N∼3.2 K. The magnetic phase diagram is understood as a successive domain reorientation and a metamagnetic phase transition for T3+ exhibits spin correlations characteristic of a type II structure but never achieves long range order.