L Journal of Alloys and Compounds 264 (1998) 38–42 Magnetic behaviour of RCuAl compounds a, a a b c * ´ ´ P. Javorsky , L. Havela ,V. Sechovsky , H. Michor , K. Jurek a Department of Metal Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2, The Czech Republic b ¨ Institut f ur Experimentalphysik, TU Wien, A-1040 Wien, Austria c ´ Institute of Physics, Czech Academy of Sciences, Cukrovarnicka 10, 162 00 Prague 6, The Czech Republic Received 7 April 1997 Abstract We studied structural and magnetic properties of the RCuAl (R5rare earth) intermetallic compounds by means of X-ray diffraction, susceptibility, magnetization and specific heat measurements. Magnetic ordering at low temperatures was observed in most of these materials. Results provide indications of ferromagnetic coupling in the heavy rare-earth compounds (R5Gd–Er), while PrCuAl and NdCuAl show antiferromagnetic behaviour. Additional magnetic phase transition in the ordered state was found in GdCuAl and DyCuAl. A metamagnetic transition was observed in DyCuAl.  1998 Elsevier Science S.A. Keywords: Rare-earth intermetallic compounds; Magnetic properties 1. Introduction perform a broader study of magnetic behaviour of the RCuAl compounds. In recent years, much of the research effort has been focused on studies of the magnetic behaviour of ternary intermetallic RTX (R5rare earth, T5transition metal, X5 2. Experimental p-metal) compounds [1]. Among the RTAl compounds, the RNiAl and RCuAl ones crystallize in the ZrNiAl-type Polycrystalline samples were prepared by arc-melting ¯ hexagonal structure (space group P62m). The RNiAl stochiometric amounts of pure elements (3 N for rare compounds have been investigated by various techniques earth, 5 N for Cu and Al) under an argon atmosphere. To (e.g., Refs. [2–4]). Complex magnetic structures in these account for evaporation losses, a 5 and 2 wt.% excess of compounds have been derived from neutron diffraction the rare-earth component was taken for TmCuAl and experiments [5–8]. On the other hand, the RCuAl com- SmCuAl, respectively. pounds have not been investigated so intensively. Basic The X-ray diffraction patterns were taken on powder information on magnetic properties has been obtained from samples at room temperature using the Cu Ka radiation. magnetization curves measured at different temperatures The microprobe analysis was performed using a mi- [2]. Further measurements on selected RCuAl compounds croanalyser JXA-733 (JEOL). The following lines have (R5Y, Ce, Gd, Tb, Er, Lu) have been reported in Refs. been selected for the analysis of individual elements: Al [5,8–11]. Detailed studies including powder neutron dif- Ka, Cu Ka,RLa (R stands for rare earth). The energy of fraction performed on ErCuAl [8] and TbCuAl [5] showed the electron beam was 15 to 20 keV. Pure elements of the that both compounds order ferromagnetically at low tem- rare earth, Cu and Al O were used as standards. The 2 3 peratures. Exceptionally large interest has been attracted weight concentrations were obtained from the measured by the mixed-valence compound YbCuAl [12]. Interesting relative intensities (i.e. ratios to the standards) using a ZAF magnetic behaviour of RNiAl compounds motivated us to method and a KEVEX program support. The magnetization and the magnetic susceptibility was measured on powder samples with grains randomly ori- * ented and fixed by glue. Measurements in the temperature Corresponding author: Fax: (420-2) 2191-1351; e-mail: javor@mag.mff.cuni.cz range 2–300 K were performed using a Faraday balance 0925-8388 / 98 / $19.00  1998 Elsevier Science S.A. All rights reserved. PII S0925-8388(97)00198-9