Spin gaps in pseudo-one-dimensional RMn4Al8 compounds (R=Y, Ce and La)

Abstract LaMn 4 Al 8 displays large amplitude spin fluctuations arising from linear chains of Mn atoms. Inelastic neutron scattering data for LaMn 4 Al 8 shows that the dynamical magnetic response has two components: a quasielastic component and a broad inelastic peak centred near 30 meV.YMn 4 Al 8 and CeMn 4 Al 8 display maxima in their susceptibilities near 500 and 300 K, respectively. This has been taken as evidence for the presence of a magnetic pseudogap in YMn 4 Al 8 , possibly arising from one-dimensional AF correlations. We report inelastic neutron scattering data for the weak magnetic response of both YMn 4 Al 8 and CeMn 4 Al 8 . In YMn 4 Al 8 a clear spin gap of order 27 meV is evident for a limited range of wavevectors. In CeMn 4 Al 8 the gap formation is less obvious, being partly masked by the intermediate-valence response of the cerium.