The in situ formation of magnetoplumbite-type (M-type) hexa-ferrites within a 3Y-TZP matrix was examined for the La2O3-ZnO-Fe2O3, and BaO-Fe2O3 systems. The formation of barium hexaferrite (Ba-M) was rapid enough at a temperature of 1300 degrees C for 2 h to result in a uniform dispersion of fine Ba-M particles in a tetragonal zirconia polycrystal (TZP) matrix. However, the formation of lanthanum-substituted hexaferrite (La-M) was rather sluggish, despite the existence of a charge-compensating divalent oxide. The 3Y-TZP/20-wt%-BaFe12O19 in situ composite possessed good magnetic properties, as well as moderately good mechanical properties.