A Complete High-to-Low spin state Transition of Trivalent Cobalt Ion in Octahedral Symmetry in SrCo_0.5Ru_0.5O_3-δ

Abstract

The complex metal oxide SrCo0.5Ru0.5O(3-δ) possesses a slightly distorted perovskite crystal structure. Its insulating nature infers a well-defined charge distribution, and the six-fold coordinated transition metals have the oxidation states +5 for ruthenium and +3 for cobalt as observed by X-ray spectroscopy. We have discovered that Co(3+) ion is purely high-spin at room temperature, which is unique for a Co(3+) in an octahedral oxygen surrounding. We attribute this to the crystal field interaction being weaker than the Hund's-rule exchange due to a relatively large mean Co-O distances of 1.98(2) Å, as obtained by EXAFS and X-ray diffraction experiments. A gradual high-to-low spin state transition is completed by applying high hydrostatic pressure of up to 40 GPa. Across this spin state transition, the Co Kβ emission spectra can be fully explained by a weighted sum of the high-spin and low-spin spectra. Thereby is the much debated intermediate spin state of Co(3+) absent in this material. These results allow us to draw an energy diagram depicting relative stabilities of the high-, intermediate-, and low-spin states as functions of the metal-oxygen bond length for a Co(3+) ion in an octahedral coordination.

Relation between the Co-O bond lengths and the spin state of Co in layered Cobaltates: a high-pressure study

“…Moreover, the line shape of the Sr 2 Co 0.5 Ir 0.5 O 4 spectrum is very different from that of EuCoO 3 , implying a different local electronic structure. As shown in previous studies, the presence of the low-energy shoulder S1 at the Co 3+ L 3 edge is characteristic for the high-spin state, while the high-energy shoulder S2 is indicative for the low-spin state 24, 29 . The similarity between Sr 2 Co 0.5 Ir 0.5 O 4 and SrCo 0.5 Ru 0.5 O 3-δ also shows the same spin state, namely HS.…”

“…1 together with those of EuCoO 3 as a LS-Co 3+ reference, SrCo 0.5 Ru 0.5 O 3-δ as a HS-Co 3+ reference, and CoO as a high-spin (HS) Co 2+   24, 29 . One can see that the center of gravity of the L 3 white line of Sr 2 Co 0.5 Ir 0.5 O 4 (red line) is at a higher photon energy as compared to that of CoO, while it is similar to that of EuCoO 3 and SrCo 0.5 Ru 0.5 O 3-δ .…”

Ba2NiOsO6 : A Dirac-Mott insulator with ferromagnetism near 100 K

“…In contrast, a spectral shift at the Os-L3 edge of approximately 1.0(1) eV to higher energy from Sr2FeOsO6 to Ba2NiOsO6 indicates an increased valency of one from Os 5+ to Os 6+ in the latter. [47][48][49][50] The energy shift, the CFS, and the relative t2g and eg related spectral weights can be clearly discerned in the second derivative spectra at the bottom of the right inset in Figure 1. The eg related peak is shifted by 1.3(1) eV to higher energy in Ba2NiOsO6 relative to Sr2FeOsO6, and the spectral weight of the t2g related peak increases reflecting a smaller number of t2g holes 47 on Os 5+ (t2g 3 ) compared to Os 6+ (t2g 2 ).…”

Magnetism and charge order in the ladder compound Co3O2BO3

“…The moments at site 4 are connected through different superexchange paths to several other magnetic ions in the structure. This results in conflicting information with [19], where the HS and LS states exchange stability. a cost in energy for the system.…”