INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 15 (2003) 2045–2052 PII: S0953-8984(03)56176-8 Study of vibrational and magnetic excitations in Ni c Mg 1-c O solid solutions by Raman spectroscopy E Cazzanelli 1 , A Kuzmin 2 , G Mariotto 3 and N Mironova-Ulmane 2 1 INFM and Dipartimento di Fisica, Universit` a della Calabria, I-87036 Arcavacata di Rende (Cosenza), Italy 2 Institute of Solid State Physics, Kengaraga Street 8, LV-1063 Riga, Latvia 3 INFM and Dipartimento di Fisica, Universit` a di Trento, I-38050 Povo (Trento), Italy E-mail: a.kuzmin@cfi.lu.lv Received 15 November 2002 Published 17 March 2003 Online at stacks.iop.org/JPhysCM/15/2045 Abstract The Raman scattering by phonons and magnons was studied for the first time in the polycrystalline solid solutions Ni c Mg 1−c O. The experimental Raman spectrum for c = 0.9 is similar to that of NiO and consists of six well resolved bands, whose origins are the disorder-induced one-phonon scattering (bands at 400 and 500 cm −1 ), two-phonon scattering (bands at 750, 900, and 1100 cm −1 ), and two-magnon scattering (the broad band at ∼1400 cm −1 ). We found that the dependence of the two-magnon band in solid solutions on the composition and temperature is consistent with their magnetic phase diagram. We also observed that the relative contribution of two-phonon scattering decreases strongly upon dilution with magnesium ions and disappears completely at c < 0.5. Such behaviour is explained in terms of a disorder-induced effect, which increases the probability of the one-phonon scattering processes. 1. Introduction Diluted antiferromagnets represent an interesting class of materials, whose crystallographic structure is closely related to their magnetic properties [1]. Recently, a correlation between long- and short-range order in solid solutions with a face-centred-cubic (fcc) magnetic sublattice has been reviewed for a number of zinc-blende- and rock-salt-type compounds [2]. In these systems, depending on the type of the host-lattice packing, the cation/anion radii ratio, and the difference in substituting ions size, the ordered-on-average crystal lattice experiences local distortions. The Ni c Mg 1−c O system provides a nice example of a diluted antiferromagnet. It forms a continuous series of solid solutions, whose magnetic properties vary with the composition from antiferromagnetic-like behaviour, with the N´ eel temperature T N = 523 K for pure NiO, 0953-8984/03/122045+08$30.00 © 2003 IOP Publishing Ltd Printed in the UK 2045