Direct Correlation between Domain Size and Coercive Force in Iron Alloys

Abstract

The Bitter technique was used to observe magnetic domain patterns on specimens of polycrystalline iron and iron containing 2.5 wt % silicon. Domain patterns that appear on grains oriented close to (110) [001] with respect to the specimen surface were observed. A critical domain size indicator S, based on measurements of domain size with the specimen in the demagnetized state, was developed and found to vary inversely with the coercive force. Values of S ranging from 0.23×10−3 cm to 1.2×10−3 cm were measured on iron specimens having coercive force values from 2.75 Oe down to 0.43 Oe. Similar results were obtained for the 2.5% Si-Fe alloy. Domain patterns were also observed under changing applied field conditions. In the region of the coercive force, ``spike'' domains annihilated one another and also joined together to form a continuous volume of reverse magnetization. The domain interactions suggest an unstable condition between domain wall energy and volume energy, followed by the interaction of domains which resulted in a lower wall energy.