Incommensurate spin correlations in highly oxidized cobaltates La$_{2-x}$Sr$_{x}$CoO$_{4}$

TL;DR

This study investigates the magnetic properties of highly oxidized layered cobaltates La$_{2-x}$Sr$_{x}$CoO$_{4}$, revealing the disappearance of hourglass magnetic spectra and the emergence of broad excitations around charge-ordered phase positions.

Contribution

It provides new insights into the magnetic excitation spectrum in highly hole-doped cobaltates, highlighting the role of inter-site exchange interactions in magnetic phase behavior.

Findings

Hourglass magnetic spectra disappear at high Sr doping.

Broad low-energy excitations are centered around charge order positions.

Strong inter-site exchange interactions are crucial for hourglass spectra emergence.

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.