Electronic properties of RX₂Al₂₀ (R  =  La, Ce, Yb, Th, U; X  =  Ti, V, Cr and Mn) cage compounds

Non-spin-polarized electronic structures and Fermi surface properties of RX₂Al₂₀ (R = La, Ce, Yb, Th, U; X = Ti, V, Cr, Mn) intermetallic compounds were calculated using the full potential all-electron local orbital (FPLO) approach in the framework of the local density approximation (LDA). Trends of the magnetism are discussed in terms of the characteristics of X-3d bands with a quantitative analysis of the relationship between band electron filling and crystal electric field splitting. Since coordination icosahedra of X-atoms have small trigonal distortion, crystal electric field splits the fivefold degenerate X-3d state into low-energy singlet a_1g and two higher-energy doublets e_g. In RTi₂Al₂₀ and RV₂Al₂₀ the population of the related 3d sub-band is not sufficient to cause energetically favorable spin polarization, whereas magnetic instabilities develop in the RCr₂Al₂₀ series. Finally, a manifestation of strong repulsive interactions between itinerant Mn-d electrons become most pronounced in ferromagnetic UMn₂Al₂₀. The influence of non-magnetic R-f states on magnetic and thermodynamic properties is discussed with special emphasis on the role of the f–p and f–d hybridization. For LaTi₂Al₂₀ and LaV₂Al₂₀ the calculated quantum oscillation frequencies are in accord with experimental reports.