F-19 NMR-STUDY OF KMNFEF6 .2. A FRUSTRATED MAGNETIC SYSTEM

F-19 NMR studies are performed in polycrystalline KMnFeF6 in the tempe rature 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-iso and K-ax, and the intr insic line width, 2 beta, of the resonance lines corresponding to the eight types of fluorines present in the unit cell are determined by de convoluting the experimental spectra in the whole temperature range. I n order to understand the behavior of the local electronic susceptibil ity around each type of fluorine site as a function of temperature, th e hyperfine contributions to the parameters K-iso and K-ax are determi ned by subtracting from these the calculated value of the dipolar cont ribution to the same at each temperature. The results clearly reveal t hat 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 i s in conformity with that predicted from the Curie-Weiss behavior of t he bulk susceptibility. However, the present results also show that th e ferromagnetic short-range correlations are developed among the magne tic ions bonded with the fluorines F(5) and F(8) below 200 K. The resu lt indicates the development of spin canting within the metal ions bon ded with F(5) and F(8) far above the ferrimagnetic transition temperat ure (T-N = 148 K).