Spectroscopic studies of magnon excitations in nanosized NiO

Nina Mironova-Ulmane 1Alexei Kuzmin 1Ints Steins 2Janis Grabis 2Ilmo Sildos 3Martti Pärs 3

1. Institute of Solid State Physics, University of Latvia, 8 Kengaraga, Riga LV-1063, Latvia
2. Institute of Inorganic Chemistry, Riga Technical University, Riga LV-2169, Latvia
3. Institute of Physics, University of Tartu, Riia str. 142, Tartu 51014, Estonia

Abstract

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 [5]. 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 [3], 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.

References:

[1] R. E. Dietz, G. I. Parisot, A. E. Meixner, Phys. Rev. B 4, 2302 (1971).

[2] M. Grimsditch, L. E. McNeil, D. J. Lockwood, Phys. Rev. B 58, 14462 (1998).

[3] E. Cazzanelli, A. Kuzmin, G. Mariotto, N. Mironova-Ulmane, J. Phys.: Condens. Matter 15, 2045 (2003).

[4] E. Cazzanelli, A. Kuzmin, G. Mariotto, N. Mironova-Ulmane, Phys. Rev. B 71, 1344151 (2005).

[5] J. Grabis, I. Steins, D. Rasmane, G. Heidemane, J. European Ceramic Soc. 17, 1437 (1997).

 

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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