Single crystal growth and magnetic properties of La2-xMxCoO4 (M = Ca, Ba)

摘要

Magnetic properties were investigated for single crystals of La2-xCaxCoO4 (0.5 <= x <= 0.8) and for polycrystalline samples of La2-xBaxCoO4 (0.5 <= x <= 0.9). In the Ca system, the effective moment mu(eff) decreased with increasing x from 4.0 mu(B) (x = 0.5) to 3.0 mu(B) (x = 0.7-0.8), accompanied by a steep reduction of Weiss temperature Theta. These drastic changes of the magnetic properties suggest a spin-state transition of the Co3+ ions from the high-spin state to the intermediate-spin state. On the other hand, the effective moment of La2-xBaxCoO4 was almost 4.0 mu B and there is no change of Weiss temperature Theta. These facts suggest that the intermediate-spin state is related to the Co-O bond length, i.e. crystal fields. (c) 2006 Elsevier B.V. All rights reserved.