The magnetic structures of double tungstates, NaM(WO4)2, M=Fe, Cr: Examples for superexchange couplings mediated by [NaO6]-octahedra

Strong magnetoelastic coupling at the transition from harmonic to anharmonic order inNaFe(WO4)2with3d5Simon1, Ackermann2, Chapon3 et al. 2016Phys. Rev. B134220View full textAdd to dashboardCite

“…The high-temperature part was fitted by the inverse Curie-Weiss function χ −1 m = C −1 (T + θ) yielding Weiss temperatures θ ranging from about -6.8 to -8.9 K depending on the field direction, see Fig.2(b), and an average effective magnetic moment µ eff,exp = 5.93 µ B , in very good agreement with the expected value of µ eff = 2 S(S + 1) µ B = 5.92 µ B for a spin-only moment of Fe 3+ with S = 5/2. The results agree with values determined from powder samples 16 .…”

“…Isotropic temperature factors and anisotropic extinction correction (model 4 in FullProf 32 ) were applied. The values for the atomic positions correspond very nicely to the results obtained from powder data 16 and the anisotropic extinction parameters reflect the plate-like shape of the crystal. The structural dataset can also be used to verify the occupation of the different atomic sites.…”

“…We show that the zero-field magnetic structure is more complex than previously proposed 16 , because it develops an incommensurate spin spiral, which, however, does not result in a multiferroic phase. Most interestingly, there are several phase transitions associated with the emergence of anharmonic components, whose signatures in some macroscopic properties (thermal expansion) are even larger than those associated with the onset of magnetic order in zero magnetic field.…”

“…1(b)). In spite of the long distance between the Fe 3+ ions in adjacent layers, NaFe(WO 4 ) 2 develops a threedimensional magnetic structure at temperatures below 4 K. The analysis of neutron powder diffraction yielded a collinear antiferromagnetic structure with magnetic moments aligned parallel to the a axis 16 . The magnetic reflections were indexed with a commensurate propagation vector k com = (0.5, 0.5, 0.5) that corresponds to an upup-down-down magnetic arrangement along the chains, which can be explained by a dominating next-nearest neighbor magnetic interaction within the chains.…”

Phase equilibria in the system NaAl(WO4)2–NaCr(WO4)2

“…The calculated cell parameters of the solid solutions in this region are presented in Table 2. The values of the cell parameters at 100 at% chromium content (pure NaCr(WO 4 ) 2 ) agree very well with those published in the literature [28]. Moreover, the values of the cell parameters linearly increase with the increase in the average effective radius of the Me 3+ ion from 0.57 Å (average effective radius at an Al:Cr ratio of 50:50), through 0.60 Å (average effective radius at an Al:Cr ratio of 30:70), to 0.615 Å (100 at% chromium).…”