Magnetic excitation in La1.5Ca0.5CoO4

Abstract We examined checkerboard charge and spin order in La 1.5 Ca 0.5 CoO 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 0.5 Sr 1.5 MnO 4 . Spin-wave dispersion at majority stacking is seen up to 16 meV, in contrast to 50 meV in La 1.5 Sr 0.5 NiO 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.