Modelling Shape-Memory Effects in Ferromagnetic Alloys

Abstract

We develop a combined Ginzburg-Landau/ micromagnetic model dealing with conventional and magnetic shape-memory properties in ferromagnetic shapememory materials. The free energy of the system is written as the sum of structural, magnetic and magnetostructural contributions. We first analyse a mean field linearized version of the model that does not take into account longrange terms arising from elastic compatibility and demagnetization effects. This model can be solved analytically and in spite of its simplicity allows us to understand the role of the magnetostructural term in driving magnetic shape-memory effects. Numerical simulations of the full model have also been performed. They show that the model is able to reproduce magnetostructural microstructures reported in magnetic shape-memory materials such as Ni 2 MnGa as well as conventional and magnetic shape-memory behaviour.

Multiferroic and Related Hysteretic Behavior in Ferromagnetic Shape Memory Alloys

“…In the present study, we use a mesoscopic approach which has been already presented in previous papers . To properly account for the multiferroic character of the Ni 2 MnGa alloy, the total free energy of the system must include both the structural and the magnetic degrees of freedom ( F S and F M , respectively) as well as a magnetostructural coupling term F M−S , which will give rise to the desired cross response of each generalized displacement to the corresponding nonconjugated field.…”

“…With these considerations, the total free energy that can be expressed in terms of the OP strain only (apart from magnetization), whose formulation makes explicit the long‐range and anisotropic character of the non‐OP contributions, favoring strain modulations along ⟨11⟩ directions. The particular expressions can be found elsewhere …”