Magnetic Manipulation of Spatially Confined Multiferroic Heuslers by Martensitic Microstructure Engineering

TL;DR

This paper demonstrates a microstructure engineering approach to control magnetic stray fields in Ni-Mn-Ga Heusler films, enabling tailored magnetic properties for smart device applications through twinning configuration manipulation.

Contribution

It introduces a post-annealing process to switch twinning configurations in epitaxial Ni-Mn-Ga films, enhancing magnetic stray fields for improved device integration.

Findings

Twinning configurations can be switched from Y-type to X-type.

Post-annealing induces significant changes in magnetic stray fields.

Advanced characterization confirms microstructure and surface quality.

Abstract

Magnetic shape-memory (MSM) Heuslers show a strong coupling between magnetic and structural characteristics, evidencing a correlation between magnetic, thermal, and mechanical properties through a magnetostructural martensitic transformation. This functional aspect makes MSM Heuslers promising for integration into smart micro/nanodevices, including sensors, energy harvesters, and actuators. Controlling the martensitic microstructure, which determines the magnetic characteristics, is among the key points for optimization of the magnetic functional properties of these materials at different length scales. Here, we report a strategy for manipulating the magnetic properties of spatially confined epitaxial Ni-Mn-Ga films grown on Cr(001)//MgO(001) by twinning configuration engineering in the low-temperature ferromagnetic (martensitic) phase. We show how the twinning configurations in the continuous films and the micropatterned structures can be switched from Y-type (showing negligible magnetic stray field) into X-type (presenting significant magnetic stray field) by a post-annealing process. Advanced characterization techniques enable us to analyze the atomic structure and the surface quality of the annealed samples and to disentangle the twin-switching phenomenon. The martensitic microstructure engineering reported in this study introduces a simple method for promoting the magnetic stray-field contribution at the surface of Ni-Mn-Ga epitaxial thin films and micropatterns initially showing a negligible magnetic stray field.