A two dimensional model for ferromagnetic martensites

TL;DR

This paper introduces a 2-D model for ferromagnetic martensites that couples strain and magnetic order parameters, revealing complex interactions affecting magnetization and strain morphology, with implications for hysteresis behavior.

Contribution

It presents a novel 2-D square-to-rectangle martensite model coupling strain and magnetic order, exploring their interplay across different temperature regimes.

Findings

Magnetic order orientation can change at interfaces.

Magnetization curves can differ from mean field predictions.

Strain morphology is influenced by magnetic order.

Abstract

We consider a recently introduced 2-D square-to-rectangle martensite model that explains several unusual features of martensites to study ferromagnetic martensites. The strain order parameter is coupled to the magnetic order parameter through a 4-state clock model. Studies are carried out for several combinations of the ordering of the Curie temperatures of the austenite and martensite phases and, the martensite transformation temperature. We find that the orientation of the magnetic order which generally points along the short axis of the rectangular variant, changes as one crosses the twin or the martensite-austenite interface. The model shows the possibility of a subtle interplay between the growth of strain and magnetic order parameters as the temperature is decreased. In some cases, this leads to qualitatively different magnetization curves from those predicted by earlier mean field models. Further, we find that strain morphology can be substantially altered by the magnetic order. We have also studied the dynamic hysteresis behavior. The corresponding dissipation during the forward and reverse cycles has features similar to the Barkhausen's noise.