Piezomagnetism of Biased Ferrites

摘要

New developments in the synthesis and processing of magnetostrictive materials that are highly piezomagnetic in the polarized state are briefly described and interpreted in terms of the relationship for reversible stress sensitivity derived by Bozorth and Williams. In the system MnOCoOFe2O3, a coupling coefficient 0.39 has been obtained for Mn0.970Co0.068Fe1.962O4 and 0.33 for Mn0.932Co0.068Fe2O4. Solid solutions of the nickel cobalt and manganese cobalt ferrites are also piezomagnetic. These materials require atmosphere control during the firing process. When similar processing is applied to the commercially established nickel cobalt ferrites, a coupling coefficient 0.42 is obtained for Ni0.974Co0.026Fe2O4 without requiring quenching from high temperatures. It is suggested that the high piezomagnetic activity of the manganese cobalt ferrites can be understood if the appropriate strain term in the expression derived by Bozorth and Williams is better identified by the easy direction magnetostriction instead of the polycrystalline magnetostriction. This interpretation leads to the prediction that magnetite with the correct cobalt ferrite addition is highly piezomagnetic.