Past exam of the materials science course of the University of Cambridge / 2018 / Paper 1 / 2 / c / i / Solution

If removal restores the original random-domain magnetic state, the magnetostrictive strain and induced voltage return toward their original values. Elastic strain transfer then relaxes the stress on the central layer.

A ferromagnetic nickel layer can retain remanent magnetization and an altered domain population, so removing the external field does not guarantee removal of all magnetostriction. The electrical time response also depends on leakage and the input impedance of the voltmeter: an open-circuit strain-induced voltage can decay through a finite resistance even while some strain remains. The final observed voltage is therefore history- and circuit-dependent.