An Accurate Determination of the Exchange Constant in Sr_2CuO_3 from Recent Theoretical Results

Data from susceptibility measurements on Sr_2CuO_3 are compared with recent theoretical predictions for the magnetic susceptibility of the antiferromagnetic spin-1/2 Heisenberg chain. The experimental data fully confirms the theoretical predictions and in turn we establish that Sr_2CuO_3 behaves almost perfectly like a one-dimensional antiferromagnet with an exchange coupling of J = 1700^{+150}_{-100}K.Comment: revised and reformatted paper with new title to appear in Phys. Rev B (Feb.1996). 3 pages (revtex) with 3 embedded figures (macro included). A complete postscript file is available from http://fy.chalmers.se/~eggert/expsusc.ps or by request from [email protected]

Stoichiometry of LiNiO2 studied by Mössbauer spectroscopy

From the 61Ni and 57Fe Mössbauer spectroscopy data follows the cationic site assignment in Li1–x Ni1+x O2. Our data explain the ferromagnetic properties of this material because of the appearance of Ni2+ (S=1) among Ni3+ (S=1/2) in Ni3+O2 hexagonal planes. We have no evidence for the ferromagnetic interaction between the NiO2 layers through the excess Ni2+ ions substituting the Li+ ions. The presence of Ni2+ found in the Ni3+O2 planes explains the absence of the Jahn–Teller distortions probably because of the electronic transfer between the Ni3+ and Ni2+ ions