Determination of structural and magnetic properties in directionally solidified Ni-Mn-Ga rod with an axial compositional variation

Abstract

A Ni-Mn-Ga alloy rod with significant axial compositional gradient has been designed by directional solidification at a low growth speed. The axial distributions of Ni and Ga gradually decrease and that of Mn gradually increases, which agrees with Burton-Prim-Slichter relationship. The axial crystal structure changes from austenite to martensite accordingly, and the crystal orientation relationship and the microstructure evolution near the phase interface have been investigated by EBSD and TEM. Moreover, the saturation magnetization along the solidification direction decreases due to the enhancement of anti-ferromagnetic coupling between Mn ions. The present research provides an alternative way not only to investigate martensite/austenite phase interface but also to explore a wide range of compositions and corresponding structures and properties in Ni-Mn-Ga alloys.