  We exploit the intrinsic structural instability of the Fe70Pd30 magnetic
shape memory alloy to obtain functional epitaxial films exhibiting a
self-organized nanostructure. We demonstrate that coherent epitaxial straining
by 54% is possible. The combination of thin film experiments and large-scale
first-principles calculations enables us to establish a lattice relaxation
mechanism, which is not expected for stable materials. We identify a low twin
boundary energy compared to a high elastic energy as key prerequisite for the
adaptive nanotwinning. Our approach is versatile as it allows to control both,
nanostructure and intrinsic properties for ferromagnetic, ferroelastic and
ferroelectric materials.
