Local magnetism and structural properties of HeuslerNi2MnGaalloys

We present a detailed experimental study of bulk and powder samples of the ferromagnetic Heusler shape-memory alloy ${\mathrm{Ni}}_{2}\mathrm{MnGa}$, including zero-field static and dynamic $^{55}\mathrm{Mn}$ NMR experiments, x-ray powder diffraction and magnetization experiments. The NMR spectra give direct access to the sequence of structural phase transitions in this compound, from the $\text{high}\ensuremath{-}T$ austenitic phase down to the $\text{low}\ensuremath{-}T$ martensitic phase. In addition, a detailed investigation of the so-called $rf\ensuremath{-}\text{enhancement}$ factor delivers the local magnetic stiffness and restoring fields for each separate structural environment, thus, differentiating signals coming from austenitic and martensitic components. In this way we can also resolve differences in the local spin moments of the two phases of the order of 0.08 Bohr magnetons, and reveal precursor phenomena of the martensitic transformation well inside the parent austenitic phase.