  Modulated phases occur in numerous functional materials like giant
ferroelectrics and magnetic shape memory alloys. To understand the origin of
these phases, we review and generalize the concept of adaptive martensite. As a
starting point, we investigate the coexistence of austenite, adaptive 14M phase
and tetragonal martensite in Ni-Mn-Ga magnetic shape memory alloy epitaxial
films. The modulated martensite can be constructed from nanotwinned variants of
a tetragonal martensite phase. By combining the concept of adaptive martensite
with branching of twin variants, we can explain key features of modulated
phases from a microscopic view. This includes phase stability, the sequence of
6M-10M-NM intermartensitic transitions, and magnetocrystalline anisotropy.
