Magnetic and thermodynamic studies on the charge and spin ordering in the highly-doped La_{2− x}Sr_xCoO₄

We report magnetic studies on the charge and spin ordering in La_{2− x}Sr_xCoO₄ for x=1/3, 0.60, and 0.75. The magnetic susceptibility displays a clear cusp which we attribute to a spin glass freezing transition in all three compositions stduied. The behaviors of the evaluated effective magnetic moment and Curie-Weiss temperature indicate that the antiferromagnetic (AFM) interaction among Co²⁺ ions surrounded by the non-magnetic Co³⁺ weakens with increasing the doping concentration x. In addition, we have found that the incommensurate AFM short range order is frozen at T_g which is further below the onset temperature T_IC of the neutron intensity of the incommensurate AFM correlation.