Magnetic excitation in La 1.5Ca 0.5CoO 4

Abstract

We examined checkerboard charge and spin order in La 1.5Ca 0.5CoO 4 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, l). The origin of magnetic scattering can be explained by the minority and majority stacking arrangement of Co 2+/Co 3+ spins along the c-axis since the same magnetic reflections arise from the two stacking vectors in La 0.5Sr 1.5MnO 4. Spin-wave dispersion at majority stacking is seen up to 16 meV, in contrast to 50 meV in La 1.5Sr 0.5NiO 4. 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.