Spin and Charge Order in Single-Layered Provskite Cobaltates

Abstract

Recent neutron scattering studies on charge and spin ordering in Pr2 xCaxCoO4 (0:39 x 0:73) and La2 xSrxCoO4 (x = 0:61) are reviewed. We found that the propagation vectors of the charge and spin order for both systems are (2 ,0,1) and ( ,0,1), respectively, in the orthorhombic notation with lattice constants a = 5:392 A and c = 12:196 A. is linearly proportional to 1 x for x > 0:5, = 1 x, but it is 0.5 for 0:39 x 0:5. This indicates that while the checkerboard charge ordered state previously observed in La2 xSrxCoO4(x = 0.5) is also realized in Pr2 xCaxCoO4 with 0:39 x 0:5 and La2 xSrxCoO4 (x = 0:61), the charge ordered state for x > 0:5 is di erent from the checkerboard order. Instead, our results suggest that for x > 0:5, a charge-density-wave-like modulation of Co2+ and Co3+ ions occurs in the Co-O plane and that ferromagnetic stripes formed at the Co2+ sites along the b-axis are antiferromagnetically arranged along the a-axis.