Theory of stripe domains in magnetic shape memory alloys

TL;DR

This paper develops a theoretical model to analyze the formation and evolution of stripe domain patterns in magnetic shape memory alloys under magnetic fields, revealing critical thickness effects on variant states.

Contribution

It introduces a geometrical domain-model considering straight stripe-like variants with fixed magnetization and derives equilibrium parameters as functions of field and material properties.

Findings

Oblique multivariant states exist only in plates thicker than a critical value.

In thinner plates, a direct transition occurs between single variant states.

The model facilitates analytical and numerical evaluation of domain configurations.

Abstract

The evolution of multivariant patterns in thin plates of magnetic shape memory materials with an applied magnetic field was studied theoretically. A geometrical domain-model is considered composed of straight stripe-like martensite variants with constant internal magnetization (high anisotropy limit) and magnetic domain wall orientation fixed by the twin boundaries. Through integral transforms of the demagnetization energy, the micromagnetic energy is cast into a form convenient for direct numerical evaluation and analytical calculations. The equilibrium geometrical parameters of multivariant patterns with straight and oblique twin boundaries have been derived as functions of the applied field and the material parameters of a plate. It is shown that the oblique multivariant states exist only in plates with thicknesses L larger than a certain critical value L_0. In samples with L < L_0 a magnetic-field-driven transformation occurs directly between single variant states.