Direct observation of double-k lattice modulation in double-k magnetic structures. The case of CeAl2
Symmetry analysis is combined with x-ray scattering experiments to investigate the lattice modulation associated with the incommensurate magnetic structure in the case of a double-k structure. The expansion of the free energy shows that the components of the magnetic structure with propagation vectors k(1) and k(2) can couple via components of lattice modulations. It is shown that the classical di