19F NMR study ofKMnFeF6. II. A frustrated magnetic system

Abstract

${}^{19}$F NMR studies are performed in polycrystalline ${\mathrm{KMnFeF}}_{6}$ in the temperature range ${T}_{N}$ (148 K) $<T<395$ K at the resonance frequencies 15 and 34 MHz. The isotropic shift and the anisotropic part of the combined (hyperfine and dipolar) shift parameters, ${K}_{\mathrm{iso}}$ and ${K}_{\mathrm{ax}},$ and the intrinsic line width, 2$\ensuremath{\beta}$, of the resonance lines corresponding to the eight types of fluorines present in the unit cell are determined by deconvoluting the experimental spectra in the whole temperature range. In order to understand the behavior of the local electronic susceptibility around each type of fluorine site as a function of temperature, the hyperfine contributions to the parameters ${K}_{\mathrm{iso}}$ and ${K}_{\mathrm{ax}}$ are determined by subtracting from these the calculated value of the dipolar contribution to the same at each temperature. The results clearly reveal that antiferromagnetic short-range correlations are developed among the magnetic ions bonded with the fluorines F(1), F(2), F(3), F(4), F(6), and F(7) below 200 K. This nature of the local exchange interaction is in conformity with that predicted from the Curie-Weiss behavior of the bulk susceptibility. However, the present results also show that the ferromagnetic short-range correlations are developed among the magnetic ions bonded with the fluorines F(5) and F(8) below 200 K. The result indicates the development of spin canting within the metal ions bonded with F(5) and F(8) far above the ferrimagnetic transition temperature ${(T}_{N}$ = 148 K).