ANTIFERROMAGNETIC BEHAVIOR IN S=2 LAYERED RBMNF4

The magnetic properties of layered-perovskite RbMnF4 have been investi gated by neutron powder diffraction. This compound exhibits a magnetic ordering below T(c) = 3.7 +/- 0.2 K. The resolution of the magnetic s tructure at 1.5 K indicates that RbMnF4 orders as a collinear antiferr omagnet. The propagation vector is k = 0 and the magnetic moment of ea ch sublattice has a value of 2.97(3) mu(B). The strong reduction of th e observed magnetic moment should be attributed to a particularly high two-dimensional character of this compound.