Evidence for the collapse of short-range magnetic order in CoO at the Néel temperature

Abstract

Auger-photoelectron coincidence spectroscopy is used for investigating the electronic properties of a CoO thin film above and below the magnetic transition temperature (TN ). By using the dichroic effect in angle-resolved measurements, we identify and assign well-defined highspin and low-spin structures in spite of the otherwise featureless Auger singles spectra, typically found for open-band systems. The disappearance of the dichroism for temperatures just above TN indicates a collapse of the surface short-range magnetic order, presumably due to a strongly reduced exchange field in the surface compared to that in the bulk.

Spin-Dependent On-Site Electron Correlations and Localization in Itinerant Ferromagnets

“…3(b) for the two geometries, and explains all of the features in the data. Following our assignment of the peaks we can describe the low energy (38 eV) peak as a triplet only and the higher energy (43 eV) one as a mixed singlet triplet in agreement to previous works [11,13,22,23]. The agreement between measured and computed spectra is very good: Theory well accounts for the presence of two peaks in the Auger energy distribution and their angular dependence in the measurements.…”

Insight on Hole-Hole Interaction and Magnetic Order from Dichroic Auger-Photoelectron Coincidence Spectra

“…Qualitatively, the different spin contents of structures A and B had been conjectured already in Ref. [25] based on a Tanabe-Sugano [27] analysis of the data. The present more quantitative work validates this picture and shows that the same occurs at lower kinetic energies too (features D and E) where a similar dichroism occurs between S ¼ 1=2 and S ¼ 3=2.…”

“…1 we also report the profile obtained by soft x rays from Ref. [25]. The lower energy of the incident photons gives rise to a rather different spectrum.…”

“…(dashed line) and our calculated Co-removal spectrum (solid line). Right panel: the spectrum excited by 250 eV x rays from Ref [25]. (dashed line) and our calculated (0:8Co þ 0:2O)-removal spectrum (solid line).…”

“…Taking into account that in the experiment of Ref. [25] no absolute calibration of the Auger energy scale was performed and that an overall uncertainty of AE0:4 eV is estimated, the energy In addition, C has a shoulder at $43 eV which is not evident in the asymmetry curve because it appears in both the S ¼ 5=2 and S ¼ 3=2 spectra, but is clearly seen in both the AN and NN data.…”