Crystal field parameters of the rare earth pyrochlores $R_2$Ti${}_2$O${}_7$ ($R$ = Tb, Dy, Ho)

Abstract

In this work we present inelastic neutron scattering experiments which probe the single ion ground states of the rare earth pyrochlores $R_2$Ti${}_2$O${}_7$ ($R$ = Tb, Dy, Ho). Dy${}_2$Ti${}_2$O${}_7$ and Ho${}_2$Ti${}_2$O${}_7$ are dipolar spin ices, now often described as hosts of emergent magnetic monopole excitations; the low temperature state of Tb${}_2$Ti${}_2$O${}_7$ has features of both spin liquids and spin glasses, and strong magnetoelastic coupling. We measured the crystal field excitations of all three compounds and obtained a unified set of crystal field parameters. Additional measurements of a single crystal of Tb${}_2$Ti${}_2$O${}_7$ clarified the assignment of the crystal field levels in this material and also revealed a new example of a bound state between a crystal field level and an optical phonon mode.

17 pages, 7 figures