B-H Loop Squareness in the Magnesium-Manganese Ferrites, 1953 October 22

MIT DIC 6889. Project Whirlwind Memo M-2473. A mechanism is proposed whereby a tetragonal 2MOMnO₂ phase is precipitated at {101} surfaces in manganese-rich spinel systems. The critical Mn[superscript +4] content for precipitation is estimated from studies of lattice parameters in the Fe₃O₄-Mn₃O₄-ZnMn₂O₄-ZnFe₂O₄ system. A prediction is then made as to which compositions in the MgO-Fe₃O₄-Mn₃O₄ system will give favorable B-H loops. A large region is found to depend critically upon the firing atmosphere as a result of the variability of the degree of ionization of both the iron and manganese ions. It is suggested that both the original reacting and final firing should be done in oxygen-free atmospheres for optimum results in this region of the compositional diagram. A relatively high electric conductivity is also predicted for materials with these compositions. Finally the theoretical predictions are compared with some preliminary experiments which are being done in the chemistry section of Group 63 under the direction of F. E. Vinal.