Magnetic Induction and Coercive Force Data on Members of the Series BaAlxFe12−xO19 and Related Oxides

Abstract

Oxides having the magnetoplumbite structure and a wide range of magnetic properties have been examined. The magnetic saturations of the compositions M^IIFe₁₂O₁₉ can be lowered by replacing part of the iron with the ions Al³⁺, Ga³⁺, Mn³⁺, Cr³⁺, and Ge³⁺ amongst others. M^II in 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 BaAl_xFe_12−xO₁₉ series. As the aluminum contents of the materials increase toward such a point, the ratio 2K/I (where K is the magnetocrystalline anisotropy constant and I is 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.