  Bi3Mn4O12(NO3), in which the Mn4+ ions carry S=3/2, is the first honeycomb
lattice system that shows no long-range magnetic order. Using neutron
scattering, we have determined that short-range antiferromagnetic correlations
develop at low temperatures. Applied magnetic fields induce a magnetic
transition, in which the short-range order abruptly expands into a long-range
order.
