Reinterpretation of physical property data for TmV2Al20

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Australian Institute of Physics
Compounds of the RM2Al20-type (R = rare earth, M = transition metal) are of interest for the study of fundamental low temperature physical and magnetic properties. Members of this series crystallise in the cubic CeCr2Al20 structure type with the space group 4d3̅m (#227). Given that the rare earth site (cubic4̅3m / Td site symmetry) is at the centre of a polyhedron of 16 Al ions [1], members of the series are referred to as ‘caged rare earth compounds’. The relatively large lattice parameter (typically of the order of 15 Å) results in a large separation of the rare earth nearest neighbours and leads to weak R-R exchange interactions. Consequently, the magnetic ordering temperature is suppressed, typically to less than 2 K. In some cases magnetic order has not yet been observed. Investigations of PrV2Al20 and PrTi2Al20 revealed interesting phenomena associated with the non-magnetic ground state of the cubic Pr3+ site. These included the quadrupolar Kondo effect [2] and superconductivity behaviour [3]. The compound TmV2Al20 is a hole analogue of PrV2Al20 and was subsequently investigated at low temperatures in search of similar or related phenomena. A key outcome of this later work [4] was that the high quality, single crystal, heat capacity data were interpreted in terms of a cubic crystal field (CF) interaction with just the two parameters, x and W, of the Lea, Leask and Wolf [5] formalism. However an additional arbitrary broadening of the CF ground state was necessary to better match the experimental data at low temperature. In order to improve on these CF results, we carried out inelastic neutron scattering and electron paramagnetic resonance measurements which better define x and W for Tm3+ in TmV2Al20 [6]. In this paper we show that in addition to this crystal field Hamiltonian, the single crystal magnetisation and specific heat data are better interpreted in terms of a model that involves partial Al flux substitution of an approximately 10% depleted Tm “cage” site; this interpretation allows inclusion of “rattling” contributions of caged Tm and Al ions in specific heat.
Crystals, Energy levels, Magnetic resonance, Physical properties, Reasonance, Scattering, Thermodynamic properties, Transition temperature
Hutchison, W. D., Stewart, G. A., White, R., Iles, G. N., Cadogan, J. M., Namiki, T., & Nishimura, K. (2020). Reinterpretation of physical property data for TmV2Al20. Poster presented to the 44th Condensed Matter and Materials Meeting, Holiday Inn, Rotorua, New Zealand 4-7 February 2020. (pp. 66). Retrieved from: