Determination of the crystal field levels in TmV2Al20

So called caged rare earth compounds of the RM Al20-type (R = lanthanide, M = transition metal) exhibit interesting physical and magnetic properties at low temperatures. For example PrV Al20 and PrTi Al20 show a quadrupolar Kondo effect [1] and superconductivity [2] brought about by the non-magnetic ground state and the cubic symmetry of the Pr3+site. In this work the compound TmV Al20, a hole analogue of PrV Al20 has been investigated. Previous crystal field calculations based on specific heat and magnetisation [3] resulted in parameters of W = 0.5 K and x = -0.6 within the Lea, Leask and Wolf formalism [4]. However to match the experimental zero field specific heat near 0.5 K, an artificial broadening of the ground state was applied. To validate and clarify these results, we have carried out an inelastic neutron scattering experiment on the PELICAN time-of-flight spectrometer to determine the energy splitting between the crystal field levels. This has allowed a further refinement of the crystal field parameters to W = 0.42(1) K and x = -0.63(1). The very broad Lorentzian line shapes suggest strong 4f-conduction band electron coupling.
Rare earth compounds, Transition elements, Magnetic properties, Superconductivity, Ground states, Neutron diffraction
White, R., Hutchison, W., Iles, G., Mole, R., Cadogan, S., Namiki, T., & Nishimura, K. (2017). Determination of the crystal field levels in TmV2Al20. Paper presented at ICNS 2017 (International Conference on Neutron Scattering), Daejeon, South Korea, 9 to 13 July 2017. Retrieved from: