MAGNETIC-PROPERTIES OF FEROXYHYTE (DELTA-FEOOH)

Magnetization curves and high-field Mossbauer spectra are used to dedu ce a model for the magnetic order in synthetic samples of delta-FeOOH (feroxyhyte), which takes account of the changes in magnetization when the samples are heated at 105 degrees C. Feroxyhyte is essentially a planar antiferromagnet with the net sublattice moments aligned paralle l or antiparallel to c. Each particle acquires a net moment due to the very small number of layers along the c-direction, and the presence o f surface steps causing the formation of ferrimagnetic domains with an odd number of layers. There is some spin canting which is related to the crystallinity of the sample. The decrease in magnetization followi ng heating is mainly due to an increase in the extent of antiferromagn etic coupling between the closely packed ferrimagnetic particles, but changes in the spin canting within the bulk may also contribute. A typ ical, rather well crystallized specimen has magnetization sigma = 14 J T(-1) kg(-1) and Curie temperature T-c = 455 K.