EFFECT OF PRESSURE ON MAGNETIC EXCITATIONS IN COO

We investigated the effect of high pressure (P less-than-or-equal-to 1 7 GPa) on magnetic excitations in CoO by Raman spectroscopy in the tem perature range 10-300 K. In addition to the strong lines at 143, 221 a nd 296 cm-1 observed previously, we also measured weak Raman features at 251, 430 and 486 cm-1, and an asymmetrical broad band centered arou nd 1040 cm-1 arising from magnetic excitations. We propose a single-io n effective Hamiltonian for Co2+ and fit the energy levels of magnetic excitations using approximate second quantization techniques. The ant iferromagnetic exchange interaction constant J2 for next-nearest neigh bors is found to scale with the bond length d according to d ln J2/d l n d = 8.0 +/- 0.5.