Magnetic properties and 119 Sn hyperfine interaction parameters of LiMn 6 Sn 6

We have synthesized LiMn 6 Sn 6 , the first RMn 6 Sn 6 compound involving an alkali metal as R element. It crystallizes in the hexagonal (P6/mmm) HfFe 6 Ge 6 -type structure. From magnetic measurements and powder neutron diffraction experiments it is found that LiMn 6 Sn 6 magnetically orders at T C =380 K in a simple easy-plane ferromagnetic structure (m Mn =2.58 μ B at 2 K). The 119 Sn Mössbauer spectrum recorded at 5 K indicates that the tin nuclei experience huge hyperfine fields (as large as 35 T). Electronic structure calculations are used to gain information about the microscopic origin of both the hyperfine field and electric field gradient at the Sn nuclei. The former arises due to spin-dependent hybridization between the 5s states of Sn and the 3d states of Mn. The latter comes from the 5p charge density close to the nucleus, whose anisotropy is mainly produced through directional interactions with the 3d states of the first Mn neighbors. Comparison between experimental quadrupole splittings and theoretical electric field gradients allows us to propose a value of $Q=- 11.2 \pm 0.7~{\rm fm}^{2}$ for the quadrupole moment of the first excited state (I= 3/2) of the 119 Sn nucleus. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006