Modulations in martensitic Heusler alloys originate from nanotwin ordering

Abstract

Heusler alloys exhibiting magnetic and martensitic transitions enable applications like magnetocaloric refrigeration and actuation based on the magnetic shape memory effect. Their outstanding functional properties depend on low hysteresis losses and low actuation fields. These are only achieved if the atomic positions deviate from a tetragonal lattice by periodic displacements. The origin of the so-called modulated structures is the subject of much controversy: They are either explained by phonon softening or adaptive nanotwinning. Here we used large-scale density functional theory calculations on the Ni2MnGa prototype system to demonstrate interaction energy between twin boundaries. Minimizing the interaction energy resulted in the experimentally observed ordered modulations at the atomic scale, it explained that a/b twin boundaries are stacking faults at the mesoscale, and contributed substantially to the macroscopic hysteresis losses. Furthermore, we found that phonon softening paves the transformation path towards the nanotwinned martensite state. This unified both opposing concepts to explain modulated martensite.

21 manuscript pages with 7 figures

References in corpus (6)

• Role of the conduction electrons in mediating exchange interactions in Heusler alloys
• Combined experimental and theoretical investigation of the premartensitic transition in Ni${}_2$MnGa
• Premartensite to martensite transition and its implications on the origin of modulation in Ni2MnGa ferromagnetic shape memory alloy
• Geometry of Adaptive Martensite in Ni-Mn-based Heusler alloys
• Ab initio prediction of stable nanotwin double layers and 4O structure in Ni${}_2$MnGa
• Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni${}_2$MnGa

Cited by in corpus (6)

• Nucleation and growth of hierarchical martensite in epitaxial shape memory films
• Building hierarchical martensite
• Geometry of Adaptive Martensite in Ni-Mn-based Heusler alloys
• Epitaxial strain adaption in chemically disordered FeRh thin films
• Bulk Electronic Structure of Ni2MnGa studied by Density Functional Theory and Hard X-ray Photoelectron Spectroscopy
• Shear Deformation of Nonmodulated Ni${}_2$MnGa Martensite: An Ab Initio Study