Magnetic and thermodynamic properties ofLi2VOSiO4:A two-dimensional

Abstract

NMR, muon spin rotation (SR), magnetization, and specific-heat measurements in Li 2 VOSiO 4 powders and single crystals are reported. Specific-heat and magnetization measurements evidence that Li 2 VOSiO 4 is a frustrated two-dimensional Sϭ1/2 Heisenberg antiferromagnet on a square lattice with a superexchange coupling J 1 , along the sides of the square, almost equal to J 2 , the one along the diagonal (J 2 /J 1 ϭ1.1Ϯ0.1 with J 2 ϩJ 1 ϭ8.2Ϯ1 K). At T c Ӎ2.8 K a phase transition to a low-temperature collinear order is observed. T c and the sublattice magnetization, derived from NMR and SR, were found practically independent on the magnetic field intensity up to 9 T. The critical exponent of the sublattice magnetization was estimated ␤Ӎ0.235, nearly coincident with the one predicted for a two-dimensional XY system on a finite size. The different magnetic properties found above and below T c are associated with the modifications in the spin Hamiltonian arising from a structural distortion occurring just above T c .

Spin freezing in the disordered pyrochlore magnet NaCaCo2F7 : NMR studies and Monte Carlo simulations

“…Such a spectrum proves a quasi-static and spatially disordered field distribution in NaCaCo 2 F 7 . Collinear and non-collinear long-range ordered states can be ruled out, because in single crystals those would induce a distinct line splitting in the ordered state [18][19][20].Analysis of the 23 Na NMR spectra 23 Na NMR spectra were taken on the geodesic between (1 1 1) and (1 0 0) directions. To describe the data, a physical model is constructed, by taking into account the crystal structure and the nearest neighbors environments.…”

Monovacancy paramagnetism in neutron-irradiated graphite probed by13C NMR

“…This is a commonly observed phenomenology in the paramagnetic limit of materials with strongly localized materials [50][51][52] For further investigation of the gapped behavior, the 1/T 1 data is plotted in logarithmic scale as a function of the reciprocal temperature 1/T in Fig. 3.…”

Magnetic excitation spectrum of the square latticeS=1∕2Heisenberg antiferromagnetK2VLumsden1, Nagler2, Sales3 et al. 2006Phys. Rev. B210260View full textAdd to dashboardCite

“…A splitting of this magnitude together with the nondegenerate orbital ground state eliminates orbital effects from playing a significant role on the mode splitting observed at much lower energies ͑ϳ3 meV͒. As a caveat, it is important to note that the crystal field splitting in K 2 V 3 O 8 has not been directly measured experimentally and the above arguments are based purely on comparison with other related vanadate systems 57,58,65 together with band structure calculations. 64 …”

“…One particular compound of note is Li 2 VOSiO 4 , 65 which has a crystal structure where V-O distances within the square pyramid are almost identical to K 2 V 3 O 8 . For this compound, an experimental estimate of the splitting between the ground state and first crystal field excited state yielded a splitting of ϳ150 meV, 65 while LDA band structure calculations estimated this value to be ϳ400 meV. 63 The local structural similarity between K 2 V 3 O 8 and these other vanadates together with the evi-dence for rather large splitting in all of these materials, is very strong evidence of splitting between the d xy ground state and the d xz , d yz lowest lying excited state for K 2 V 3 O 8 which is on the order of hundreds of meV.…”