Anisotropic susceptibility of La2-xSrxCoO4 related to the spin states of cobalt

We present a study of the magnetic susceptibility of La2-xSrxCoO4 single crystals in a doping range 0.3 <= x <= 0.8. Our data show a pronounced magnetic anisotropy for all compounds. This anisotropy is in agreement with a low-spin ground state (S = 0) of Co3+ for x >= 0.4 and a high-spin ground state (S = 3/2) of Co2+. We compare our data with a crystal-field model calculation assuming local moments and find a good description of the magnetic behavior for x >= 0.5. This includes the pronounced kinks observed in the inverse magnetic susceptibility, which result from the anisotropy and low-energy excited states of Co2+ and are not related to magnetic ordering or temperature-dependent spinstate transitions.