Electron density distribution in paramagnetic and antiferromagnetic CoO: A γ-ray diffraction study

Abstract

Highly accurate single-crystal structure factors, complete up to sin /ϭ1.6 Å Ϫ1 , have been measured from CoO at 305 K and in the antiferromagnetic state at 10 K using 316.5 keV ␥ radiation. Moderate uniaxial pressure was applied in the low-temperature phase to force a single-T-domain sample. A detailed description of the electron-density distribution is presented. The occupancies of the 3d shell are computed from multipole refinement parameters, showing significant differences between the two magnetic phases. The spin and orbital contributions to the total magnetic moment of Co are derived from the experimentally determined number of unpaired electrons. Results are compared with ab initio calculations as well as with magnetic form factor measurements. A careful analysis of electronic properties in the internuclear regions reveals the Co-O interaction to be purely ionic. Its physical significance on the antiferromagnetism is discussed.

Metal-insulator and magnetic transition of NiO at high pressures

“…22͒ and CoO. 23 Figure 2 shows the schematic plot for the ionization and affinity energies of NiO. The energy difference between occupied e g and t 2g orbitals without hybridization with ligand oxygen ions is determined by U 0 ϪUЈϪ⌬ CF , in which U 0 is the Coulomb repulsion energy between two electrons with opposite spins on the same d orbital, UЈ the repulsion energy for two electrons on different d orbitals, ⌬ CF the crystal-field splitting.…”

Using hysteresis behaviour to determine the anisotropy and interactions in complex self-assembled Co metallic nanoparticle systems

“…A method to reduce the oxide shell is the exposure to mild reactive hydrogen plasma resulting in metallic Co particles [4]. Since the lattice constants of FCC Co (a ¼ 0:35447 nm) and FCC CoO (0.42614 nm) [5] are different, the particles shrink. Applying this technique we have obtained a sample ( Fig.…”

Doping of cobalt oxide with transition metal impurities:Ab initiostudy

“…35,36 Very often another, magnetic state of CoO is in the focus of research: a AF-II exists below the Néel temperature T N = 290 K. 35 In this structure magnetic moments of Co within same ͕111͖ sheet of a cubic cell are aligned parallel to each other but antiparallel to the moments in adjacent sheets, so the magnetic propagation vector Q II in the cubic unit cell of AF-II structure is ͓0.5,0.5,0.5͔. Recent high-resolution x-ray diffraction studies 35,36 revealed tetragonal distortion along the edges of the Fm3m unit-cell cube with c / a = 0.988 accompanied by a small trigonal deformation along the ͓111͔ direction. 35 These lattice distortions change the crystal symmetry from tetragonal to monoclinic with an angle of 89.962°between the two edges of a different length.…”