High-magnetic-field NMR studies ofLiVGe2O6:A quasi-one-dimensional spin

Abstract

We report7 Li pulsed NMR measurements in polycrystalline and single crystal samples of the quasi one-dimensional S = 1 antiferromagnet LiVGe2O6, whose AF transition temperature is TN ≃ 24.5 K. The field (B0) and temperature (T ) ranges covered were 9-44.5 T and 1.7-300 K respectively. The measurements included NMR spectra, the spin-lattice relaxation rate (T −1 1 ), and the spin-phase relaxation rate (T −1 2 ), often as a function of the orientation of the field relative to the crystal axes. The spectra indicate an AF magnetic structure consistent with that obtained from neutron diffraction measurements, but with the moments aligned parallel to the c-axis. The spectra also provide the T -dependence of the AF order parameter and show that the transition is either second order or weakly first order. Both the spectra and the T −1 1 data show that B0 has at most a small effect on the alignment of the AF moment. There is no spin-flop transition up to 44.5 T. These features indicate a very large magnetic anisotropy energy in LiVGe2O6 with orbital degrees of freedom playing an important role. Below 8 K, T −1 1 varies substantially with the orientation of B0 in the plane perpendicular to the c-axis, suggesting a small energy gap for magnetic fluctuations that is very anisotropic.

NMR and dc susceptibility studies ofNaVGe2O6

“…Moreover, both compounds contain chains of VO 6 -octahedra, kept apart by GeO 4 -tetrahedra [7]. Previously, we and other authors reported dc-susceptibility and NMR studies on LiVGe 2 O 6 [7][8] [9]. The results turned out to be qualitatively the same as those for NaVGe 2 O 6 reported in this work.…”

“…The uncertainity is, in particular, due to the fact that in the calculations we considered only dipolar coupling. In addition, the moments need not be aligned along the same direction, and their magnitude might also be reduced (as was suggested in the case of LiVGe 2 O 6 , see [9]). …”

“…It has been concluded that the low-temperature phase is antiferromagnetically ordered, with a ferromagnetic interchain coupling; the magnitude of the ordered moments was reported to be 1.14µ B , a much smaller value than expected from the gfactor inferred from the susceptibility. Using the above value for the ordered moment and single crystal NMRexperiments results, the authors of [9] suggested that the ordering occurs along the c-axis. Our data are consistent with a similar scenario for NaVGe 2 O 6 .…”

Magnetic ordering and spin structure in Ca-bearing clinopyroxenes CaM2+(Si, Ge)2O6, M=Fe, Ni, Co, Mn

“…This is mainly due to a distinct low-dimensional (quasi-one-dimensional) character of the atomic arrangements within edge-sharing MO 6 chains, bearing the magnetic ions, and the fact that in some compounds spin-gap behaviour has been found. Such compounds are LiTi 3+ Si 2 O 6 and NaTi 3+ Si 2 O 6 [3,4], but also LiV 3+ Ge 2 O 6 [5][6][7] and CaCu 2+ Ge 2 O 6 [8][9][10][11] were intensively studied in terms of low-dimensional magnetic behaviour at low temperatures. While some compounds have a spin-gap ground state others exhibit welldeveloped three-dimensional (3D) antiferromagnetic (AFM) ordering such as LiFe 3+ Si 2 O 6 [12], or (Li, Na)V 3+ (Si, Ge) 2 O 6 ( [13,14]; also ferromagnetic (FM) ordering is found e.g.…”

Detection of magnetic order in theS=1chain compoundLiVGe2OBlundell1, Steer2, Pratt3 et al. 2003Phys. Rev. B190120View full textAdd to dashboardCite

“…15 X-ray and neutron-diffraction experiments 15 showed that no distortion takes place, but indicated a second-order phase transition to an AF state, a result which is in agreement with a recent high-field NMR study. 16 In this paper, we demonstrate, using muon-spin rotation experiments, that LiVGe 2 O 6 undergoes a second-order phase transition to an AF state. We observe that the local magnetic field at the muon sites is quasistatic on the muon time scale.…”