Magnetic susceptibility, X-ray diffraction, and electron-spin resonance studies were carried out for the calcium-doped lithium-sodium cobaltite Li0.42Na0.36CazCoO2 ( z = 0.02; 0.04). The evolution of the cell parameters with increasing calcium content in Li0.42Na0.36CazCoO2 was considered. Phases with different calcium concentrations were found to exhibit a large diversity of susceptibilities. Spin dimer analysis was performed to explain the anomalous magnetic behavior of the calcium-rich phase. (C) 2012 Elsevier B. V. All rights reserved.