Enhancement of two-magnon scattering in annealed nickel oxide studied by Raman spectroscopy

Abstract

Laser Raman spectroscopy is used to study the enhancement effect of two-magnon scattering in nickel oxide through annealing treatment in a temperature range from 450 ℃ to 1050 ℃, and investigate laser heating effect on two-magnon scattering. Our study shows that two-magnon scattering of nickel oxide can be tremendously enhanced with annealing temperature rising. In the temperature range from 450 ℃ to 1050 ℃, the enhancement increases with annealing temperature increasing, and with 1050 ℃ annealing the two-magnon scattering can be enhanced more than two orders of magnitude, also the enhancement of two-magnon scattering is much stronger than that of two-phonon scattering. This tremendous enhancement is correlated not only with the significant decrease of Ni-vacancy by high temperature annealing, but also with the magnetic spin ordering network of Ni ions. The variation of sensitive intensity of two-magnon scattering with the concentration of Ni-vacancy can be used to provide a simple Raman spectroscopy method of quantitatively measuring the Ni-vacancy in nickel oxide. In addition, the annealing treatment can significantly reduce the laser heating effect on two-magnon scatting in nickel oxide power samples. At low annealing temperature, the intensity of two-magnon scattering quickly quenches with increasing laser power. With 1050 ℃ annealing, the laser heating effect on two-magnon scattering is significantly reduced and two-magnon scattering can still have strong intensity at high laser power.