Electronic structure and magnetic interactions

– We present results of all-electron electronic structure calculations for the recently discovered d electron heavy fermion compound LiV2O4. The augmented spherical wave calculations are based on density functional theory within the local density approximation. The electronic properties near the Fermi energy originate almost exclusively from V 3d t2g states, which fall into two equally occupied subbands: While σ-type metal-metal bonding leads to rather broad bands, small π-type p–d overlap causes a narrow peak at EF. Without the geometric frustration inherent in the crystal structure, spin-polarized calculations reveal an antiferromagnetic ground state and ferromagnetic order at slightly higher energy. Since direct d–d exchange interaction plays only a minor role, ordering of the localized vanadium moments can be attributed exclusively to a rather weak superexchange interaction. With the magnetic order suppressed by the geometric frustration, the remaining spin fluctuations suggest an explanation of the low temperature behaviour of the specific heat. The magnetic porperties of the metallic spinel structure transition metal oxide LiV 2 O 4 have remained an unresolved issue for some time [1, 2, 3, 4]. Apart from a temperature independent contribution, the susceptibility was found to follow a Curie-Weiss law due to local V magnetic moments [3, 4]. The negative Weiss temperature of-63 K indicates antiferromagnetic exchange interactions between the vanadium spins [3]. However, a transition to long-range magnetic order above 1.8 K could be excluded from both susceptibility and 7 Li NMR measurements [4, 5]. This apparent contradiction was attributed to possible geometric frustration inherent in the vanadium sublattice of the normal spinel structure with only nearest neighbour interaction, which might prohibit long-range antiferromagnetic order [4, 6]. Recently, Kondo et al. reported a crossover from localized moment to heavy Fermi liquid behaviour with a Kondo temperature of T K ≈ 28 K and an electronic specific heat coefficient of γ ≈ 0.42J/molK 2 at 1 K [5, 7]. Thus for the first time heavy fermion (HF) behaviour, characteristic of f electron systems, has been observed in a d electron material. Below 30 K, the resistivity exhibited a pronounced smooth downturn consistent with Kondo lattice behaviour [5]. The nearly temperature independent susceptibility and the 7 Li Knight shift Typeset using EURO-T E X