Synthesis and magnetic properties of new beta " alumina-like ferrites

Single crystals of a rhombohedral ferrite Na/sub 1.4/K/sub 0.5/Fe/sub 10.9/Zn/sub 0.9/O/sub 17/ have been synthesized using a flux method. According to an X-ray study, the ferrite is isotypic with beta " alumina. Magnetization measurements have been performed on a single crystal. This ferrite is a noncompensated antiferromagnetic compound; T/sub c/=475 degrees C. The weak ferrimagnetic components depends significantly on the exact chemical composition of the compound; at 4.2 K, M/sub 0/=9 emu/g for the crystal studied. New compounds derived from this beta " ferrite have been obtained by ion exchange in molten salts. After annealing at 950 degrees C, the barium exchanged compound is isotypic with the M hexagonal ferrite; its refined chemical formula is BaFe/sub 11.8/Zn/sub 0.2/O/sub 18.9/. T/sub c/ is about 450 degrees C and M/sub s/=64.5 emu/g at 4.2 K. The magnetization direction is along the c-axis and the anisotropy field is about H/sub a/=11 kOe at 4.2 K.<
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