Control of Texture in Magnetic Material by Surface Energy

Abstract

Different crystallographic planes, at a gas‐metal interface, have different surface energies. Although the energy difference is small (less than 100 erg/cm²), it is sufficient to cause migration of boundaries between grains of different (hkl) surfaces provided there is a sufficiently small restraint to boundary migration. Since the (110) plane is the plane of lowest surface energy γ in 3% silicon‐iron, grains with (110) planes at the gas‐metal interface are favored to grow at the expense of other (hkl) grains (γ110<γhkl) when the material and annealing atmosphere are free of impurities. In the presence of certain impurities, however, γ100 may be lower than γhkl and grains with (100) planes are favored to grow at the expense of all others. With proper processing, sharp (110)[001] or (100)[001] textures may be obtained in sheets of high‐purity silicon‐iron. Grain size and texture can be altered by deliberate additions of oxide film to the surface, by the amount of silicon in the alloy, and by the choice of annealing atmosphere. The effect of improved texture and low impurity concentration on magnetic properties is discussed.