Synthesis, characterization, and magnetic susceptibility of the heavy-fermion transition-metal oxideLiV2O4

Abstract

The preparative method, characterization, and magnetic susceptibility measurements versus temperature T of the heavy-fermion transition-metal oxide LiV 2 O 4 are reported in detail. The intrinsic (T) shows a nearly T-independent behavior below ϳ30 K with a shallow broad maximum at Ϸ16 K, whereas Curie-Weiss-like behavior is observed above ϳ50-100 K. Field-cooled and zero-field-cooled magnetization M obs measurements in applied magnetic fields Hϭ10Ϫ100 G from 1.8 to 50 K showed no evidence for spin-glass ordering. Crystalline electric field theory for an assumed cubic V point group symmetry is found insufficient to describe the observed temperature variation of the effective magnetic moment. The Kondo and Coqblin-Schrieffer models do not describe the magnitude and T dependence of with realistic parameters. In the high-T range, fits of (T) by the predictions of high-temperature series expansion calculations provide estimates of the V-V antiferromagnetic exchange coupling constant J/k B ϳ20 K, g factor gϳ2, and the T-independent susceptibility. Other possible models to describe the (T) are discussed. The paramagnetic impurities in the samples were characterized using isothermal M obs (H) measurements with 0ϽHр5.5 T at 2-6 K. These impurities are inferred to have spin S imp ϳ3/2-4, g imp ϳ2, and molar concentrations of 0.01-0.8 %, depending on the sample.

Orbital state and magnetic properties ofLiV2O4

“…As mentioned before, a temperature dependent spin susceptibility χ(T) is observed in the temperature range from 50 to 1000 K, which fits well to the CurieWeiss law 4,7,9,10,11,12,13,15,16,17,19,20,22,23,24,25,26,27,28,29,30 χ(T)=χ 0 +C/(T-θ). However, depending on the quality of samples and experimental techniques, the values of the Curie constant C obtained from fitting the experimental data are in the range from 0.329-0.468 cm 3 K/mol.…”

“…LiV 2 O 4 exhibits a paramagnetic Curie-Weiss susceptibility 4,7,9,10,11,12,13,15,16,17,19,20,22,23,24,25,26,27,28,29,30 χ(T ) = C/(T − θ) + χ 0 in the temperature range 50-1000 K. The best fit to the experimental data is obtained under the assumption that the magnetic susceptibility χ(T ) is the sum of a Curie-Weiss and a T -independent part χ 0 , which contains Pauli paramagnetic, core diamagnetic and orbital Van Vleck contributions to the total susceptibility. 17 If all V-3d electrons (1.5 per V ion) would equally contribute to the formation of a local moment, one would expect a mixture of S = 1 and S = 1/2 vanadium ions and consequently an effective paramagnetic moment 2.34.…”

“…No magnetic ordering was observed down to 0.02 K. 9 These unexpected phenomena entailed numerous experiments, which confirmed the HF behavior of LiV 2 O 4 in a variety of physical quantities: Johnston et al 9 carried out specific heat and thermal expansion measurements. Kondo et al 11 described the synthesis, characterization and magnetic susceptibility versus temperature. Onoda et al 12 explored spin fluctuations and transport in the spinel systems Li x Mg 1−x V 2 O 4 and Li x Zn 1−x V 2 O 4 through measurements of x-ray diffraction, electrical resistivity, thermoelectric power, magnetization, and nuclear magnetic resonance (NMR).…”

New physics in frustrated magnets: Spin ices, monopoles, etc. (Review Article)

“…There the formal valence of V ion is 3.5, and the one of Fe on B sites is 2.5 (the valence of Fe ions on A sites is 3), i.e., they have to exist in equal combinations of V 3+ and V 4+ , or Fe 2+ and Fe 3+ . Notice, however, that recent studies contradict the direct application of the ice (tetrahedron) rule to LiV 2 O 4 and Fe 3 O 4 [61,62,63,64,65,66,67,68,69,70,71,72,73,74,75]. For the recent reviews on spinel materials consult, e.g., [76,77,78,79].…”

“…Among spinels with different cations at B-sites we can distinguish the situation, in which the valency of ions is different from integer, like in the first non-rare-earth based heavy-fermion system LiV 2 O 4 see, e.g., [61,62,63,64,65,66,67,68,69,70], or in, probably, the oldest known magnetic material, magnetite, Fe 3 O 4 see, e.g., [1,58,59]. There the formal valence of V ion is 3.5, and the one of Fe on B sites is 2.5 (the valence of Fe ions on A sites is 3), i.e., they have to exist in equal combinations of V 3+ and V 4+ , or Fe 2+ and Fe 3+ .…”