Abstract
The ferromagnetic spinel MgO·3MnFe2O4, ``magnesium manganese ferrite'' is satisfactory for magnetic memory devices. Small rings of about 55-mil diameter which have proved practical for memory matrix use have a coercive force of about 3 oersteds and switch-over time of 0.3 microsecond, and a nearly rectangular hysteresis loop. Rings of about 0.5-cm diameter which were used to study composition variables showed a lower coercive force of 1.6 oersteds for the same composition and processing. Resistivities are in the order of 45×103 ohm cm.