Magnetic and thermodynamic studies on the charge and spin ordering in the highly-doped La2− xSrxCoO4

We report magnetic studies on the charge and spin ordering in La2− xSrxCoO4 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 Tg which is further below the onset temperature TIC of the neutron intensity of the incommensurate AFM correlation.