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Abstract:
We observe quasi-static incommensurate magnetic peaks in neutron
scattering experiments on layered cobalt oxides La2-xSrxCoO4 with high
Co oxidation states that have been reported to be paramagnetic. This
enables us to measure the magnetic excitations in this highly hole-doped
incommensurate regime and compare our results with those found in the
low-doped incommensurate regime that exhibit hourglass magnetic spectra.
The hourglass shape of magnetic excitations completely disappears given
a high Sr doping. Moreover, broad low-energy excitations are found,
which are not centered at the incommensurate magnetic peak positions but
around the quarter-integer values that are typically exhibited by
excitations in the checkerboard charge ordered phase. Our findings
suggest that the strong inter-site exchange interactions in the undoped
islands are critical for the emergence of hourglass spectra in the
incommensurate magnetic phases of La2-xSrxCoO4.
