2003/04/15 by Claudia Bungaro, Karin M. Rabe, K. M. Rabe +2 · 1 citation
Materials Science · Physics and Astronomy · #Heusler alloys: electronic and magnetic properties #Magnetic Properties and Applications #Shape Memory Alloy Transformations #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevb.68.134104
submitted to Phys. Rev. B
arxiv created 2003/04/15 · openalex publication_date 2003/10/08 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The phonon-dispersion relations and elastic constants for ferromagnetic Ni2MnGa in the cubic and tetragonally distorted Heusler structures are computed using density-functional and density-functional-perturbation theory within the spin-polarized generalized-gradient approximation. For 0.9<c/a<1.06, the TA2 transverse- acoustic branch along [110] and the symmetry-related directions exhibit a dynamical instability at a wave vector that depends on c/a. Through examination of the Fermi-surface nesting and electron-phonon coupling, this is identified as a Kohn anomaly. In the parent cubic phase the computed tetragonal shear elastic constant, C^\ensuremath'=(C11\ensuremath-C12)/2, is close to zero, indicating a marginal elastic instability towards a uniform tetragonal distortion. We conclude that the cubic Heusler structure is unstable against a family of energy-lowering distortions produced by the coupling between a uniform tetragonal distortion and the corresponding [110] modulation. The computed relation between the c/a ratio and the modulation wave vector is in excellent agreement with structural data on the premartensitic (c/a=1) and martensitic (c/a=0.94) phases of Ni2MnGa.