Formula omitted] MAS NMR of KNiF 3: unexpected spin density at the potassium and first MAS NMR experiments in the antiferromagnetic state

Abstract

39 K MAS NMR spectra of KNiF 3 were measured at variable temperature between 180 and 450 K. In the paramagnetic state (450–270 K), a shift of the 39 K resonance to lower frequency is observed with decreasing temperature which is due to an isotropic hyperfine interaction with A iso=−(0.30±0.05)×10 −6 cm −1. This is in contrast to theory which predicts zero unpaired electron density at the potassium. In the antiferromagnetic state (below 250 K), a reduction of the shift contribution from the unpaired electrons is observed. The temperature dependence of the 39 K shifts parallels that of the magnetic susceptibilities over the whole temperature range measured.