Evidence of magnetic phase separation in LuFe2O4

The magnetic properties of a polycrystalline sample of LuFe2O4 have been investigated by means of magnetization measurements combined with neutron scattering, between 1.5 and 300 K. Magnetic Bragg peaks appear below T-N = 240 K and can be indexed in a monoclinic cell, using two propagation vectors, k(1) = (0 2/3 0)(m) and k(2) = (0 2/3 1/2)(m) [or k'(2) = (0 2/3 1/6)(m)], which correspond to either a ferromagnetic or an antiferromagnetic stacking of the [Fe2O4](infinity) bilayers. A modeling of possible magnetic structures evidences in addition that the coupling within a bilayer can be either ferromagnetic or antiferromagnetic. Results point out a complex magnetic ground state, which can be understood as coexisting antiferromagnetic and ferrimagnetic phases with a large axial magnetic anisotropy of about 8 meV.