INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 13 (2001) 3533–3543 www.iop.org/Journals/cm PII: S0953-8984(01)19671-2 A high energy inelastic neutron scattering investigation of the Gd–Fe exchange coupling in Gd 2 Fe 17 D x (x = 0, 3 and 5) O Isnard 1 , A Sippel 2 , M Loewenhaupt 2 and R Bewley 3 1 Laboratoire de Cristallographie, associ´ e` a l’Universit´ e J Fourier et ` a l’INPG, CNRS, F-38042 Grenoble, France 2 Technische Universit¨ at Dresden, Institut f ¨ ur Angewandte Physik (IAPD), D-01062 Dresden, Germany 3 ISIS, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK E-mail: isnard@polycnrs-gre.fr, astrid.sippel@gmx.net, michael.loewenhaupt@physik.tu-dresden.de and r.i.bewley@rl.ac.uk Received 1 December 2000, in final form 15 February 2001 Abstract The structural and magnetic properties of the Gd 2 Fe 17 D x compounds (x = 0, 3, and 5) have been investigated by means of x-ray powder diffraction, high energy inelastic neutron scattering and magnetic measurements. The Gd 2 Fe 17 D x compounds crystallize in the R−3m space group with the Th 2 Zn 17 - like structure. The increase of the lattice parameters with D content reveals a two-step filling of the interstitial sites with deuterium first filling the octahedral 9e sites for x = 3 and then partially filling the tetrahedral 18g sites for x = 5. The evolution of the J ex exchange coupling versus the deuterium (D) content is discussed. Although it is well known that the permanent magnet properties of D-doped samples are considerably better than those of the pure compound Gd 2 Fe 17 there is a reduction in the Gd–Fe exchange field. Finally, the influence of deuterium insertion on the exchange interaction between the Gd and Fe sublattice is compared to that of nitrogen (N) or carbon (C). The C and N atoms are found to be more efficient in reducing the intersublattice coupling. (Some figures in this article are in colour only in the electronic version; see www.iop.org) 1. Introduction The study of the physical properties of the rare-earth (R)–transition metal (T) intermetallic compounds is a major field of research in solid state physics. Some of these compounds have industrial uses, such as SmCo 5 or the Nd 2 Fe 14 B phases which are produced for permanent magnet purposes. The knowledge of the inter-sublattice exchange interaction is of major interest in order to have access to a better understanding of the fundamental properties governing the R–T 0953-8984/01/143533+11$30.00 © 2001 IOP Publishing Ltd Printed in the UK 3533