Oxides having the magnetoplumbite structure and a wide range of magnetic properties have been examined. The magnetic saturations of the compositions MIIFe12O19can be lowered by replacing part of the iron with the ions Al3+, Ga3+, Mn3+, Cr3+, and Ge3+amongst others. MIIin the above formula can be Ba2+, Sr2+, or Pb2+. Calcium can replace these ions in part. Even the samples with magnetic saturations below 200 gauss can be prepared as crystallographically oriented compacts. Contrary to its behavior in ferrites, Ga3+does not appear to occupy tetrahedral sites in the magnetoplumbite structure.Evidence is presented for the occurrence of points of magnetic compensation in the BaAlxFe12−xO19series. As the aluminum contents of the materials increase toward such a point, the ratio 2K/I(whereKis the magnetocrystalline anisotropy constant andIis the saturation magnetization) also increases. As a consequence the ferromagnetic resonance frequencies associated with the materials move to higher frequencies, and extremely high coercive forces are realized.