Magnetic excitation in La1.5Ca0.5CoO4

We examined checkerboard charge and spin order in La1.5Ca0.5CoO4 by elastic and inelastic neutron scattering. We discovered the sharp magnetic peaks with l = half-integer and broad magnetic peaks with l = integer in (0.5, 0,1). The origin of magnetic scattering can be explained by the minority and majority stacking arrangement of Co2+/Co3+ spins along the c-axis since the same magnetic reflections arise from the two stacking vectors in La0.5Sr1.5MnO4. Spin-wave dispersion at majority stacking is seen up to 16 meV, in contrast to 50meV in La1.5Sr0.5NiO4. This indicates a much weaker exchange interaction in the cobaltates than in nickelates. The dispersion at majority stacking has almost a same one with that of minority stacking. (c) 2006 Elsevier B.V. All rights reserved.