Pergamon Solid State Communications, Vol. 89, No. 6, pp. 519-522, 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038 - 1098/94 $6.00 + .00 EFFECT OF NITROGENATION ON THE MAGNETIC PROPERTIES OF Y2Fel7_xMx COMPOUNDS, WITH M = A1, Ga OR Si Mihaela Valeanu, N. Plugaru and E. Burzo* Institute of Atomic Physics, P.O. Box MG-06, Magurele, Bucharest, Romania (Received 31 August 1993 by P. Burlet) Results of X-ray diffraction studies and magnetic measurements performed on Y2Fel7_xM x compounds with M = AI, Ga or Si as well as on their nitrides are reported. The lattice constants of Y2Fel7_xMx compounds increase when Fe is substituted by AI or Ga and decrease when Fe is replaced by Si. By nitrogenation of the samples, the lattice parameters increase significantly. The volume effect on the variation of Curie temperatures in Y2Fe17_xMxNy compounds decreases when Fe is substituted by A1, Ga or Si. Magnetization data evidence a linear dependence of the mean iron moment on the Curie temperatures in the nitrides. 1. INTRODUCTION THE MAGNETIC properties of R2Fel7 compounds are strongly influenced when introducing nitrogen in the lattice [1]. The Curie temperatures and satu- ration magnetizations were found to be substantially increased. In addition the anisotropy is changed. Consequently, the R2FeI7Ny compounds were exten- sively investigated from a fundamental point of view as well as for their use as permanent magnets [2]. It is also of interest to analyse the magnetic properties of pseudobinary RE(FeM)I7Ny systems where M is a nonmagnetic metal. These studies may give informations on the magnetic behaviour of iron as well as on the exchange interactions, in nitro- genated compounds. In this paper we analyse the effect of Fe substitution by M = A1, Ga and Si on the magnetic properties of Y2Fel7_xMx compounds as well as their nitrogenated counterparts. The Y2Fel7 compound crystallizes in the Th2Nil7- type structure with the symmetry of the P63/mmc space group. In this lattice the iron atoms occupy four types of sites (6g, 12j, 12k and 4f). The exchange interactions are dependent on the distances between Fe atoms [3], changing sign at dc ~ 2.45 A. Thus, the magnetic interactions between Fe(4f)-Fe(4f) are strongly negative, while those between Fe(6g)- * Faculty of Physics, University of Cluj-Napoca, M. Kogalniceanu str., No. l, 3400 Cluj-Napoca, Romania. Fe(12k), Fe(6g)-Fe(12j) and Fe(12k)-Fe(12k) are weakly negative. The interactions associated with Fe atoms situated at distances larger than ,-~ 2.45/~ are positive. The negative interactions are not satisfied and consequently, a large magnetic energy is stored. This brings about the low ordering temperature of the above compound, Tc ,,, 310 K. The expansion of the lattice parameters by nitrogenation diminishes the negative exchange interactions, leading to a substan- tial increase of the Curie temperature. An increase of the saturation magnetization is also observed [4, 5]. 2. EXPERIMENTAL The samples were prepared by arc melting the constituent elements in purified argon atmosphere. The ingots were wrapped in tantalum foil and vacuum annealed at temperatures between 850°C and 950°C for two weeks. The X-ray data were obtained on powdered samples, by using CuK~ radiation, both before and after nitrogenation. The nitrogenation of the samples, grounded to particles with average size less than 30#m, was performed in a quartz tube, in purified nitrogen flow, at temperatures between 500-550°C, during 2 h. The formation of free iron, in small amounts, particularly in the samples treated at 550°C was evidenced. Consequently, for each substituting M element it was necessary to make a compromise, when setting the nitrogenation conditions, between the maximum nitrogen uptake and the minimum quantity of free 519