Journal of Magnetism and Magnetic Materials 71 (1988) 269-278 269 North-Holland, Amsterdam MAGNETIC AND STRUCTURAL PROPERTIES OF A NOVEL TERNARY HYDRIDE: Nd2Fe17H x (0 < x < 5) Bernhard RUPP a,. and Giinter WIESINGER b a Institutfflr Physikalische Chemie der Universitiit Wien, IViihringerstraJ3e 42, A-1090 Vienna, Austria b Institut f~r Experimentalphysik, Technische Universiti2"t Wien, Wiedner Hauptstrafle 8-10, A-1040 Vienna, Austria Received 28 September 1987 We report on structural and magnetic properties of a novel ternary hydride, Nd2Fe17H x (0 < x < 5), by means of X-ray diffraction, magnetization measurements, and M~ssbauer spectroscopy. The hydrides retain the rhombohedral symmetry of the parent compound Nd2Fe17 (Th2Zn17 type structure, space group R3m), however, the lattice expansion is found to be highly anisotropic. The magnetic ordering temperature of the hydrides is strongly increased by 67 K per hydrogen atom. While the magnetization remains practically unaffected, the hydrogen induced rise in the 57Fe hyperfine field is more pronounced. After hydrogen uptake, the isomer shift shows the typical change to more positive values. A preferential occupation of hydrogen in the lattice is suggested. 1. Introduction During the past few years ternary alloys (borides) containing neodymium and iron have gained considerable interest due to the fact that alloys of the nominal composition NdxsFevTBs provide the most promising new material ("Neomax") for the production of sintered high coercivity permanent magnets (see e.g. the recent review on this topic by Buschow [1]). The follow- ing methods have been applied in order to gain the small particles required for the production of high performance permanent magnets: mechanical grinding or milling of as cast material under pro- tective atmospheres (Sagawa et al. [2,3]), rapid solidification (melt spun alloys, Croat et al. [4]), the so-called Liquid Dynamic Compaction method (Tanigawa et al. [5]), and ternary diffusion reac- tions (Stadelmaier et al. [6]). In addition to these well-established methods powder decrepitation due to the absorption of hydrogen was recently era- * Present address and correspondence: Institut fiir Festkrr- perforschung, KFA Jiilich, D-5170 Jtilich 1, Fed. Rep. Germany. ployed by Harris et al. [7,8]. McGuiness et al. [9], and Oesterreicher and Abache [10] as a less con- ventional way to attain the required small particle size. The hydrogen sorption properties of ternary Nd-Fe-B alloys have recently been reviewed by Rupp et al. [11]. The successful application of the powder de- crepitation method raised the interest in the fundamental correlations between hydrogen ab- sorption and the magnetic properties in these al- loys. Various studies have already been performed by Oesterreicher and Abache [10], Oesterreicher and Oesterreicher [12], l'Hrritier et al. [13], Dalmas de Reotier et al. [14], Pourarian et al. [15], and Cadogan and Coey [16] in order to achieve this goal. By means of M0ssbauer spectroscopy, mag- netization measurements, and anisotropy studies Wiesinger et al. [17,18] investigated the influence of hydrogenation on the permanent magnetic properties of NdasFe77B8. The authors report on a total hydrogen induced increase in the magnetiza- tion at room temperature of 10% compared to a rise of only 6% in the 57Fe hyperfine field. On the other hand the magnetic anisotropy was found to be strongly reduced upon hydrogenation which 0304-8853/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)