Abstract
Neutron scattering and ultrasonic methods have been used to study the lattice dynamics of two
single crystals of Ni-Mn-In Heusler alloys close to Ni50Mn34In16 magnetic superelastic composition.
The paper reports the experimental determination of the low-lying phonon dispersion curves and the
elastic constants for this alloy system. We found that the frequencies of the TA2 branch are relatively low and it exhibits a small dip anomaly at a wave number n= 1/3, which softens with decreasing temperature. Associated with the softening of this phonon, we also observed the softening of the shear elastic constant C0 = (C11 ¡ C12)=2. Both temperature softenings are typical for bcc based solids which undergo martensitic transformations and re°ect the dynamical instability of the cubic lattice against shearing of f110g planes along h1¹10i directions. Additionally, we measured low-lying phonon dispersion branches and elastic constants in applied magnetic fields aimed to characterize the magnetoelastic coupling.
