Extended moment formation and magnetic ordering in the trigonal chain compound Ca3Co2O6

Abstract

The results of electronic structure calculations for the one-dimensional magnetic chain compound Ca 3 Co 2 O 6 are presented. The calculations are based on density functional theory and the local density approximation and used the augmented spherical wave (ASW) method. Our results allow for deeper understanding of recent experimental findings. In particular, alternation of Co 3d low-and high-spin states along the characteristic chains is related to differences in the oxygen coordination at the inequivalent cobalt sites. Strong hybridization of the d states with the O 2p states lays ground for polarization of the latter and the formation of extended localized magnetic moments centered at the high-spin sites. In contrast, strong metal-metal overlap along the chains gives rise to intrachain ferromagnetic exchange coupling of the extended moments via the d 3z 2 −r 2 orbitals of the low-spin cobalt atoms.

Valence, spin, and orbital state of Co ions in one-dimensionalCa3Co2O6: An x-ray absorption and magnetic circular dichroism study

“…This result supports the analysis of the Co 2p core-level x-ray photoemission spectra 15 and band-structure calculations 16,18 . In order to resolve the spin-state issue, we now resort to XMCD.…”

Heat-capacity anomalies in the presence of high magnetic fields in the spin-chain compound, Ca3Co2O6

“…In this respect, the family of compounds of the type (Sr,Ca) 3 ABO 6 (A, B= a metallic ion), forming in the K 4 CdCl 6 -derived rhombohedral structure, is of interest, as this structure consists of chains formed by face-sharing AO 6 trigonal prisms and BO 6 octahedra with A/B ions forming a triangular lattice in the basal plane [1]. Among these, the compound, Ca 3 Co 2 O 6 , is of special significance as brought out in many recent publications and has generated theoretical interests as well [1][2][3][4][5][6][7][8][9][10][11][12][13][14]:…”

Characterization and electronic structure calculations of the antiferromagnetic insulatorCa3FeRhO6

“…In particular, the obtained total magnetic moment per sublattice is smaller than the experimental value deduced from Fig. 1 as was also observed for Ca 3 Co 2 O 6 [12,13].…”

“…Adding to the 3d moment they lead to the formation of extended localized moments already observed in Ca 3 Co 2 O 6 [12] and confirm the formal Fe S = 5/2 configuration, hence, the formal Fe 3+ state. The highspin behavior at the iron sites is clearly observed in the partial DOS shown in Fig.…”

“…Nonetheless, the ferromagnetic coupling along the chains is probably related to this "spin state ordering", the latter resulting from the different crystalline electrical fields in each Co 3+ polyhedron. Such a coupling is likely to involve both LS Co 3+ and O ions [11,12,13]. In that respect, the different magnetic behavior of the two isostructural compounds Ca 3 FeRhO 6 and Ca 3 CoRhO 6 is worth mentioning [14,15,16,17,18,19,20,21].…”