The magnetic structure of vivianite, Fe3(PO4)2.8H2O

Abstract
The magnetic structure of vivianite, Fe3(PO4)2.8H2O has been determined from a single crystal neutron study. The structure is antiferromagnetic but not collinear; an angle of 42 degrees exists between the spin directions on the FeI and FeII sublattices. The noncollinear aspects of the proposed structure have been confirmed by Mossbauer measurements with the specimen in an external magnetic field. The temperature dependence of the neutron magnetic reflections indicate a Neel temperature of 8.84+or-0.05 K; no evidence is found for any long range magnetic order above this temperature. The values of the effective fields at the iron nuclei at 1.3 K are 175 kG(FeI) and 275 kG (FeII).