Co(II) Optical Absorption in Spinels: Infrared and Ligand-Field Spectroscopic Study of the Ionicity of the bond. Magnetic Structure and Co2+→Fe3+MMCT in Ferrites. Correlation with the Magneto-Optical Properties

F Hochu,M Lenglet

doi:10.1155/1998/16871

Abstract

The analysis of the infrared and ligand field spectra of COM2O4spinels reveals that the ionicity of these compounds varies in the following order aluminate > gallate > ferrite and chromite > rhodite and cobaltite. A linear relation has been established between the Δ(LO-TO)1splitting, Racah parameter and the ionic-covalent parameterSSp=ΣICP+tetra∑ICPocta. The influence of strong superexchange interactions on the optical spectrum of cobalt ferrites has been studied. The cation distribution has been established by EXAFS and XANES measurements. The cluster (CoFeO10)15–is characterized by a large MMCT transition Co2+→Fe3+at 1.65–1.7 eV (FWMH: 1.35–1.95 eV). The4A2→4T1(P) tetrahedral cobalt(II) in ferrimagnetic compounds is overlapped by the MMCT band. This study and the reinvestigation of the iron(III) electronic spectrum is ferrites may explain the magneto-optical properties of mixed cobalt-ferrites.

Highlights

Application of cobalt ferrite as high density magneto-optical recording media has been demonstrated since about 15 years
In this paper, we present a reinvestigation of the vibrational and optical properties of cobalt(II) spinels in correlation with a new parameter introduced by Portier et al [1]: the ioniccovalent parameter of cations based on polarizing power and electronegativity
Another purpose of this paper is the study of the influence of superexchange interactions on the optical spectra of substituted cobalt(II) ferrites and more precisely on the Co2+--Fe3+ metalmetal charge transfer (MMCT) located at 1.7 eV

Summary

INTRODUCTION

Application of cobalt ferrite as high density magneto-optical recording media has been demonstrated since about 15 years. In this paper, we present a reinvestigation of the vibrational and optical properties of cobalt(II) spinels in correlation with a new parameter introduced by Portier et al [1]: the ioniccovalent parameter of cations based on polarizing power and electronegativity (this parameter accounts for the iono-covalent nature of chemical bonds permitting coherent interpretation of electronic properties). Another purpose of this paper is the study of the influence of superexchange interactions on the optical spectra of substituted cobalt(II) ferrites and more precisely on the Co2+--Fe3+ metalmetal charge transfer (MMCT) located at 1.7 eV. Li0.sFe2.O4 and the study of the optical properties of Co(II) spinels allow a quantitative evaluation of the contribution of both chargetransfer and crystal-field transitions to the magneto-optical properties of different substituted cobalt ferrites in the range 0.5-2.5 eV

EXPERIMENTAL

RESULTS AND INTERPRETATION

Fe Optical Spectra and Magnetism in Oxides

10 Dq field