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Spectroscopic studies of magnon excitations in nanosized NiO
|Nina Mironova-Ulmane 1, Alexei Kuzmin 1, Ints Steins 2, Janis Grabis 2, Ilmo Sildos 3, Martti Pärs 3|
1. Institute of Solid State Physics, University of Latvia, 8 Kengaraga, Riga LV-1063, Latvia
Magnon excitations in pure nickel oxide (NiO) were successfully probed in the past by Raman spectroscopy [1,2]. Recently we have extended these studies to NicMg1−cO solid solutions [3,4], where unpredicted behavior of temperature and composition dependences of one-magnon excitation energies has been observed.
In this work, we present the Raman scattering in nanosized NiO powders, produced by the plasma synthesis . Single-crystal NiO, grown by the method of chemical transport reactions on MgO(100) substrate, was also used for comparison. Raman experiments were conducted in a wide range of temperatures from 10 to 300 K.
The Raman spectrum of single-crystal NiO shows several bands in the probed region above 400 cm-1. The first four bands have vibrational origin and, according to assignment in , correspond to one-phonon (1P) TO and LO modes (at ~570 cm-1), two-phonon (2P) 2TO modes (at ~730 cm-1), TO + LO (at ~906 cm-1) and 2LO (at ~1090 cm-1) modes. The last strongest band at 1490 cm-1 is due to a two-magnon (2M) scattering. It was observed that the intensity of two-magnon band decreases rapidly in nano-sized NiO. This effect is attributed to a decrease of antiferromagnetic spin correlations and leads to the antiferromagnetic-to-paramagnetic phase transition.
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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium A, by Nina Mironova-Ulmane
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-11 11:23 Revised: 2009-06-07 00:44