Adaptive modulations of martensites

TL;DR

This paper reviews and generalizes the concept of adaptive martensite to explain the origin and features of modulated phases in functional materials, supported by experimental analysis of Ni-Mn-Ga alloys.

Contribution

It introduces a generalized framework of adaptive martensite incorporating twin variant branching to explain modulated phase properties.

Findings

Modulated martensite can be modeled as nanotwinned variants of tetragonal martensite.

The framework explains phase stability and intermartensitic transition sequences.

The approach accounts for magnetocrystalline anisotropy in modulated phases.

Abstract

Modulated phases occur in numerous functional materials like giant ferroelectrics and magnetic shape memory alloys. To understand the origin of these phases, we review and generalize the concept of adaptive martensite. As a starting point, we investigate the coexistence of austenite, adaptive 14M phase and tetragonal martensite in Ni-Mn-Ga magnetic shape memory alloy epitaxial films. The modulated martensite can be constructed from nanotwinned variants of a tetragonal martensite phase. By combining the concept of adaptive martensite with branching of twin variants, we can explain key features of modulated phases from a microscopic view. This includes phase stability, the sequence of 6M-10M-NM intermartensitic transitions, and magnetocrystalline anisotropy.