We have investigated cobaltite relatives of the layered perovskite cuprates
and nickelates, Pr2βxβCaxβCoO4β (0.39β€xβ€0.73) and
La2βxβSrxβCoO4β (x=0.61), using elastic neutron scattering. We have
discovered doping-dependent incommensurate short-range ordering of charges and
magnetic moments, which in cobaltites occur in the range of heavy doping, 0.5β²xβ²0.75. The charge order exists already at room temperature
and shows no change on cooling. The incommensurability of its propagation
vector, Qcβ=(Ο΅cβ,0,l), roughly scales with the concentration
of Co2+ ions, Ο΅cββΌ(1βx). Magnetic order is only established
at low Tβ²40 K and has twice larger periodicity, indicating a dominant
antiferromagnetic correlation between the nearest Co2+ spins.Comment: 4 pages 4 figure