Magnetic properties in a high continuous magnetic field of the 'frustrated' compound Fe3F8(H2O)2

The new hydrated mixed-valence fluoride FeIIFe2IIIF8(H2O)2 presents an 'idle-spin behaviour' attributed to a topological frustration: the magnetic ordering of the FeIII sublattice occurs at TN=157 K whereas the FeII spins only order below 36 K. In this work, the magnetic properties of polycrystalline samples in the 1.6-300 K temperature range are presented. From magnetic susceptibility experiments, the Curie constant is found, above 200 K, to be smaller than the free-ions value. Under high continuous magnetic fields up to 200 kOe, characteristics are observed: in the 1.6-24 K temperature range a very abrupt transition attributed to the FeII-spin reorientation is found; it is characterised by a large-field hysteresis. To explain this magnetic behaviour, a magnetic structure is proposed and exchange integrals are evaluated. All this work confirms the importance of the role of the frustration.