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Abstract

We have studied the magnetic cluster compound Nb6F15 which has an odd number of 15 valence electrons per (Nb6F12)(3+) cluster core, as a function of temperature using nuclear magnetic resonance, magnetic susceptibility, electron magnetic resonance and neutron powder diffraction. Nuclear magnetic resonance of the F-19 nuclei shows two lines corresponding to the apical Fa-a nucleus, and to the inner F-i nuclei. The temperature dependence of the signal from the F-i nuclei reveals an antiferromagnetic ordering at T < 5 K, with a hyperfine field of similar to 2 mT. Magnetic susceptibility exhibits a Curie-Weiss behavior with T (N) similar to 5 K, and mu (eff) similar to 1.57 mu(B) close to the expected theoretical value for one unpaired electron (1.73 mu(B)). Electron magnetic resonance linewidth shows a transition at 5 K. Upon cooling from 10 to 1.4 K, the neutron diffraction shows a decrease in the intensity of the low-angle diffuse scattering below Q similar to 0.27 (-1). This decrease is consistent with emergence of magnetic order of large magnetic objects (clusters). This study shows that Nb6F15 is paramagnetic at RT and undergoes a transition to antiferromagnetic order at 5 K. This unique antiferromagnetic ordering results from the interaction between magnetic spins delocalized over each entire (Nb6F (12) (i) )(3+) cluster core, rather than the common magnetic ordering.