  We reinterpret neutron scattering and Raman spectroscopy experiments in
La(2-x)Sr(x)CuO(4), showing modulation of spin and lattice degrees of freedom
both in the low-temperature orthorhombic and tetragonal phases, in terms of a
magneto-elastic coupling between noncollinear configurations for the copper
spins and the oxygen octahedra. The magneto-elastic coupling furthermore
explains the recently discovered magnetic-field induced untwinning in
La(2-x)Sr(x)CuO(4), for x<2%, and allows us to understand why in
La(2-x-y)Sr(x)Nd(y)CuO(4) with y=0.4 and x=1/8, for example, when (1,0) and/or
(0,1) static spin spirals are stabilized due to hole frustration, the atomic
modulation in the low-temperature tetragonal phase of La(2-x-y)Sr(x)Nd(y)CuO(4)
has a periodicity of 4 lattice spacings, half the magnetic one.
