Magnetostriction in transversely isotropic hexagonal crystals

The simultaneous occurrence of direct and inverse magnetostriction in transversely isotropic hexagonal crystal is theoretically investigated. Particular emphasis is here given to the need of identifying the fourth-order magnetostriction tensor, as it represents the most primitive object from which all related physical quantities of interest in micromagnetism are deduced. For hexagonal crystals, the magnetostriction tensor is expressed in terms of six independent magnetostrictive coefficients whose values are, so far, unknown. Indeed, the existing literature provides just four independent constraints that are extracted from the expression of the differential scalar strain in a given direction. In this work, the two extra conditions required to solve this identification problem are obtained by deducing the explicit functional dependence of the main features characterizing the motion of a magnetic domain wall along the major axis of a thin magnetostrictive nanostrip placed on the top of a thick piezoelectric actuator. The results of our analysis reveal that such two conditions may be associated to the effective anisotropy coefficient and the domain-wall width. To validate our proposal, a comparison with some recent experimental results is also successfully addressed.