Surface enhancement of soft-mode transformation in Ni2MnGa

Abstract

Ni2 MnGa exhibits both shape memory behavior, owing to a diffusionless structural transformation, and ferromagnetism, leading to magnetic-field based actuator applications. The current interest in highly miniaturized mechanical devices raises the question whether the structural phase transformations of Ni2 MnGa are affected by the presence of interfaces. Thermal diffuse scattering of x-rays from the soft phonon mode which drives the transformation was analyzed for depths from 3.5 nm to 6.4 μm beneath a clean (001) surface. The authors find an enhancement of the transition temperature by about 15 K in the near-surface region, but no evidence for a change of the soft-mode polarization. © 2007 ..