Crystal Structure and Charge-Ordering in La_1.5Ca_0.5CoO₄ Studied by Neutron and Resonant X-ray Scattering

Spin and orbital states inLa1.5Sr0.5CoO4studied by electronic structure calculations

“…29,30 The Co 2+ -Co 3+ charge order was also observed in La 1.5 Ca 0.5 CoO 4 and the Co 3+ ions were suggested to be in a mixed IS+ HS state. 31,32 In contrast, a magnetic susceptibility study of La 2−x Sr x CoO 4 ͑0.3Յ x Յ 0.8͒ and crystal-field model calculations indicated that the Co 3+ must be in the LS state for x Ն 0.4. 21 In particular, a very recent x-ray absorption spectroscopic study by Chang et al established a picture of HS Co 2+ and LS Co 3+ for La 1.5 Sr 0.5 CoO 4 , and their study well accounts for the extremely insulating nature of the La 2−x Sr x CoO 4 series, the high charge ordering temperature and low T SO of La 1.5 Sr 0.5 CoO 4 .…”

Significant softening ofc66and hidden order parameter in the magnetic ordered state ofLa2−xHorigane1, Kobayashi2, Suzuki3 et al. 2008Phys. Rev. B4020View full textAdd to dashboardCite

“…͑Even at x = 0.5, the distortion from tetragonal symmetry is very small. 19,20 ͒ ͑2͒ The Co 2+ spin configuration of the CoO 2 plane below T N , as shown in Fig. 7, has been proved.…”

“…In fact, the crystal structure of the specimen with x = 0.5 is slightly deformed from tetragonal to orthorhombic symmetry at room temperature. 19,20 In this case, the two-dimensional representation is divided into two one-dimensional irreducible representations, which allows both a softening of c 66 and a hardening of c 11 −c 12 2 with different transition temperatures. It is interesting that both the hardening of c 11 −c 12 2 and the magnetic scattering due to Co 3+ spin order appear only when x = 0.5.…”

Antiferromagnetic Order of the Co2+ High-Spin State with a Large Orbital Angular Momentum in La1.5Ca0.5CoO4

“…13) Orthorhombic notation is used in this paper; the space group is A2mm and the lattice parameters are a $ b ¼ 5:416 Å and c ¼ 12:469 Å at room temperature. 15) The a-and b-axes cannot be measured separately even when utilizing synchrotron radiation. 15) Therefore, the a-and b-axis domains mix in the crystal.…”

“…Magnetic susceptibility 12,13) and X-ray absorption spectroscopy (XAS) 14) measurements also indicated that the spin state of Co ions change at x ¼ 0:5, although the spin state of Co 3+ exhibits inconsistency. At x ¼ 0:5, the average valence becomes 2.5+, and Co 2+ and Co 3+ ions form a checkerboard-type charge ordering, 15) and two antiferromagnetic phases (T N $ 55 K) have been reported to coexist, 13,15) although the underlying Co electronic structures remain unclear. XAS and linear-dichroic XAS can element-selectively estimate the valence and symmetry of the orbitals in the average electronic structures, but cannot estimate the spatial ordering of the valences and orbitals.…”