Journal of Alloys and Compounds 363 (2004) 63–67 Magnetic properties of DyCuSi and HoCuSi studied by neutron diffraction and magnetic measurements A. Ole´ s a , R. Duraj b , M. Kolenda c , B. Penc c , A. Szytula c,∗ a Faculty of Physics and Nuclear Technology, AGH-University of Science and Technology, Reymonta 19, 30-059 Kraków, Poland b Institute of Physics, Technical University of Cracow, Podchorazych 1, 30-084 Kraków, Poland c M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland Received 28 March 2003; received in revised form 12 May 2003; accepted 12 May 2003 Abstract Neutron diffraction and magnetic studies of polycrystalline DyCuSi and HoCuSi (crystallizing in the hexagonal Ni 2 In-type structure) indicate that below the Néel temperature equal to 11 K for DyCuSi and 9 K for HoCuSi the compounds are antiferromagnets. The Dy 3+ and Ho 3+ magnetic moments form sine-wave modulated structures described by the propagation vectors k = (k x , 0, k z ). The magnetic ordering is stable in the temperature range between 1.4 K and T N . © 2003 Elsevier B.V. All rights reserved. Keywords: Rare earth compounds; Neutron diffraction; Magnetic structure; Magnetic measurements 1. Introduction The crystal structure and magnetic properties of the RCuSi (R = rare earth) compounds have been reported in several investigations [1–13]. These compounds crystallize within two types of crystal structure depending on the an- nealing temperature. The high-temperature phase adopts the AlB 2 -type structure (space group P6/mmm) with R atoms at 1(a): 0, 0, 0 and Cu/Si atoms statistically distributed at 2(d): 1 3 2 3 1 2 ; 2 3 1 3 1 2 [2]. The low-temperature phase crystallizes in the Ni 2 In-type [3,4] (space group P6 3 /mmc) with Ni at 2(a): 0, 0, 0; 0, 0, 1 2 and 2(c) : 1 3 , 2 3 , 1 4 ; 2 3 , 1 3 , 3 4 and In at 2(d): 1 3 , 2 3 , 3 4 ; 2 3 , 1 3 , 1 4 . The R, Cu and Si atoms are located at the 2(a), 2(c) and 2(d) sites, respectively (see Fig. 1). Magnetic measurements of the RCuSi compounds with Nd, Gd, Tb, Dy and Ho (the AlB 2 -type structure) carried out in the temperature range 77–650 K [5–8] indicate that these compounds are paramagnets with magnetic moments close to the free R 3+ ion values. The new low temperature mea- surements show the presence of ferromagnetic ordering with ∗ Corresponding author. Tel.: +48-12-632-4888x5546; fax: +48-12-633-7086. E-mail address: szytula@if.uj.edu.pl (A. Szytula). Curie temperatures equal to 14 K (R = Pr), 49 K (R = Gd) and 47 K (R = Tb) [9]. Neutron diffraction experiments performed on the RCuSi (R = Tb, Dy and Ho) compounds with the Ni 2 In-type struc- ture showed that the compounds with R = Dy and Ho do not order down to 4.2 K, whereas TbCuSi orders antiferro- magnetically below T N = 16 K with a transversal amplitude modulated structure with the propagation vector k = ( 1 / 20 , 0, 1 2 ) [10]. The magnetic ordering in ErCuSi is described by the propagation vector k = ( 1 / 12 , 0, 0). The mag- netic structure can be described by a transverse sine-wave modulated arrangement of the Er moments which is squared to an anti-phase-domain structure below T = 3.5 K [11]. The data for TmCuSi are inconsistent. Firstly, on the basis of neutron diffraction data a ferromagnetic ordering was reported below T c = 9K [12]. New data stated the presence of ferromagnetic ordering below T c = 5.8 K and then a sine-wave modulated structure with the propagation vector k = (0.078, 0, 0) in a narrow temperature range up to the Néel temperature T N = 6.5 K [13]. The present paper revises the results concerning the mag- netic properties of DyCuSi and HoCuSi reported in Ref. [10] and reports some new magnetic and neutron diffraction measurements. On the basis of these data magnetic prop- 0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8388(03)00481-X