Abstract
One‐magnon and two‐magnon excitations in superparamagnetic nanocrystalline nickel oxide (NiO) with an average crystallite size of ∼2–3 nm is studied using infrared and raman spectroscopy. Nanocrystalline NiO with an average crystallite size of ∼2–3 nm was synthesized through a two‐step process. An infrared transmission spectrum of the sample was recorded in the range 15–60 cm−1. Over and above the one‐magnon excitation at 34 cm−1 the spectra shows a strong low frequency absorption peak at ∼23 cm−1 which is identified as a surface magnon excitation. Room temperature Raman spectra of the sample shows that the two‐magnon excitation is shifted by about 50 cm−1 towards the lower wavenumber side. The observations are explained in terms of the large surface to volume ratio of the samples together with the varied spin arrangements at the surface.
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