Magnetic annealing of manganese‐ferrous ferrites and nickel‐ferrous ferrites has produced memory cores with lower temperature coefficients and higher disturb ratios than conventional square‐loop ferrites. Fifty-mil diam toroids of the composition 0.5 NiFe2O4·0.5 Fe3O4switch in approximately 1 &mgr;sec with a constant 1‐amp driving current, and have disturb ratios greater than 0.7 over the range −55° to +100°C. Physical reasons for the improved properties are discussed.