Effect Of Finite Size On One-magnon And Two-magnon Excitations In Nanocrystalline NickelOxide Studied Using Infrared And RamanSpectroscopy

摘要

One-magnon and two-magnon excitations in superparamagnetic nanocrystallinenickel oxide (NiO) with an average crystallite size of –2-3 nm is studied using infrared andraman spectroscopy. Nanocrystalline NiO with an average crystallite size of –2-3 nm wassynthesized through a two-step process. An infrared transmission spectrum of the sample wasrecorded in the range 15 - 60 cm-1. Over and above the one-magnon excitation at 34 cm 1 thespectra shows a strong low frequency absorption peak at –23cm 1 which is identified as a surfacemagnon excitation. Room temperature Raman spectra of the sample shows that the two- magnonexcitation is shifted by about 50 cm-1 towards the lower wavenumber side. The observations areexplained in terms of the large surface to volume ratio of the samples together with the variedspin arrangements at the surface.