Optical spectroscopy in CoO: Phononic, electric, and magnetic excitation spectrum within the charge-transfer gap

Article

关键词: TRANSITION-METAL OXIDES;    LATTICE-DYNAMICS;    COBALT OXIDE;    LOW-TEMPERATURES;    AC CONDUCTIVITY;    MIXED CRYSTALS;    SHELL-MODEL;    NIO;    MNO;    HEAT;   

DOI  :  10.1103/PhysRevB.78.245103

来源: SCIE

【 摘 要 】

The reflectivity of single-crystalline CoO has been studied by optical spectroscopy for wave numbers ranging from 100 to 28 000 cm(-1) and for temperatures 8 < T < 325 K. A splitting of the cubic IR-active phonon mode on passing the antiferromagnetic phase transition at T-N=289 K has been observed. At low temperatures the splitting amounts to 15.0 cm(-1). In addition, we studied the splitting of the cubic crystal-field ground state of the Co2+ ions due to spin-orbit coupling, a tetragonal crystal field, and exchange interaction. Below T-N, magnetic-dipole transitions between the exchange-split levels are identified, and the energy-level scheme can be well described with a spin-orbit coupling lambda=151.1 cm(-1), an exchange constant J=17.5 cm(-1), and a tetragonal crystal-field parameter D=-47.8 cm(-1). Already in the paramagnetic state electric-quadrupole transitions between the spin-orbit split level have been observed. At high frequencies, two electronic levels of the crystal-field-split d manifold were identified at 8 000 and 18 500 cm(-1).

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