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Abstract:
The mixed-valence terbium (III/IV) fluoride KTb3F12
crystallizes with the tetragonal symmetry, space group I4/m.
Below T-N=3.6+/-0.1 K this compound exhibits an
antiferromagnetic collinear structure with k=0 characterized by
ferromagnetic chains of edge-sharing Tb4+ polyhedra and an
antiferromagnetic order between the nearest chains. The
magnetic moments of the Tb4+ ions deduced from neutron
diffraction are equal to 6.95(4) mu(B) at 1.4 K and aligned
along the c axis. The Tb3+ ions lie in a special position with
zero magnetic moments due to a symmetry cancellation effect of
the internal molecular field. In other words, Tb3+ ions present
a zero time-averaged magnetic moments in the ordered state,
whereas T-N corresponds to the long-range antiferromagnetic
ordering of the moments of the Tb4+ ions. From the thermal
variation of the reciprocal magnetic susceptibility a molar
Curie constant of 27.97(1) emu K mol-1 has been obtained, in
good agreement with the theoretical value of 27.64 expected for
two Tb4+ and one Tb3+ free ions. The Tb4+ contribution to the
magnetization is approximated by the Langevin function and then
the Tb3+ contribution is obtained by subtracting the calculated
Tb4+ contribution to the total magnetization. (C) 2002 American
Institute of Physics.
