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

Single crystals of a rhombohedral ferrite Na_1.4K_0.5Fe_10.9Zn_0.9O₁₇ 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_c=475 degrees C. The weak ferrimagnetic components depends significantly on the exact chemical composition of the compound; at 4.2 K, M₀=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_11.8Zn_0.2O_18.9. T_c is about 450 degrees C and M_s=64.5 emu/g at 4.2 K. The magnetization direction is along the c-axis and the anisotropy field is about H_a=11 kOe at 4.2 K.