Inelastic Neutron Scattering Study of Crystal Field Excitations in spin-chain compounds K2RENb5O15 (RE = Ce, Pr, Nd)

K2RENb5O15 (RE = rare earths), which form in tetragonal tungsten-bronze structure, display interesting magnetic properties arising from 1D linear spin-chain of RE3+ ions along the c-axis. The magnetic susceptibility measurements show absence of long-range magnetic ordering in K2RENb5O15 with RE = Ce, Pr, Nd down to 1.8 K. The fit to high temperature susceptibility gives Curie-Weiss temperature of -94.5 K, -62.2 K and -70.3 K for RE=Ce, Pr and Nd, respectively. However the low temperature susceptibility reveals the dominant ferromagnetic correlations for Ce and Nd, and dominant antiferromagnetic correlations for Pr. The isothermal magnetization reflects significant reduction in saturation magnetization due to strong crystal electric field (CEF) effect. Information about the CEF excitations is highly desired to understand the relation between the CEF and magnetic properties of these compounds. We therefore propose to carry out inelastic neutron scattering measurement on K2RENb5O15 (RE = Ce, Pr, Nd) using MARI