  We report on Raman scattering measurements of the A-site ordered YBaMn2O6 in
the wide temperature range of 10-650K. Upon cooling almost all phonon modes
show pronounced temperature dependencies of frequency, linewidth, and
scattering intensity. This suggests that the octahedra tilting, Mn-O bond
angles and lengths vary with temperature in a concerted way. The remarkable
feature is that the high-temperature metallic and the charge and orbital
ordered (CO-OO) states coexist down to T_N=195K. In the antiferromagnetic state
zone-folded modes are induced by the CO-OO superstructure and the phonon modes
undergo an anomalous softening and narrowing. Our results evidence that the
CO-OO state is stabilized by the spin ordering for temperatures below T_N.
