Structure and properties of some new Th compounds P. Manfrinetti a , A. Palenzona a , S.K. Dhar b, *, C. Mitra b a INFM and Dipartimento di Chimica e Chimica Industriale, Universita di Genova, Sezione di Chimica Fisica, Via Dodecaneso 31-16146, Genova, Italy b Condensed Matter Group, T.I.F.R., Homi Bhabha Road, Mumbai 400 005, India Received 4 January 1999; accepted 22 April 1999 Abstract We report the synthesis and some physical properties of four Th-based compounds ThCoGe, ThNiGe, ThCuAl 3 and ThNiAl 3 . These compounds, are to our knowledge, being reported here for the ®rst time. We observe Pauli paramagnetic behaviour in all the four compounds (with possible exception of ThCoGe), which shows that the 3d-derived electronic bands are ®lled by charge transfer. No signature of superconductivity is observed down to 1.4 K in these materials. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Intermetallics, miscellaneous; B. Crystallography; B. Magnetic properties 1. Introduction The synthesis of new Th based compounds is often of interest. Some compounds of Th become super- conductors at low temperatures, the study of which is interesting in itself. The existence of new Th compounds suggests the possible occurrence of the corresponding U analogues which may be studied for their magnetic and possible superconducting behaviour. In this work we report the synthesis of four Th based compounds ThCoGe, ThNiGe, ThCuAl 3 and ThNiAl 3 . For the ®rst two the existence of analogous U compounds, viz. UCoGe and UNiGe [1] is already known. We have measured the magnetisation, low temperature heat capacity and the electrical resistivity of these com- pounds and ®nd them to be Pauli paramagnetic. In the case of ThCoGe, magnetisation data indicate possible weak ferromagnetism setting in at about 200 K. Our present data do not establish whether the observed behaviour is intrinsic to ThCoGe or arises from the presence of a minor ferromagnetic impurity phase. The alloys were prepared from commercially supplied metals: Th 99.8 wt% purity from Metal Crystals and Oxides Ltd. UK, Co and Ni 99.99 wt% purity from Aldrich Chem. Co., USA, Cu, Ge and Al 99.999 wt% purity from Koch-Light Laboratories, UK. Turnings of Th, freshly prepared under pure argon, were mixed with ®lings of other constituents and cold pressed in a steel die. For ThCoGe and ThNiGe the pellets were melted under pure argon in an arc furnace on a water-cooled copper hearth, turned upside-down and remelted three times. In the case of ThNiAl 3 and ThCuAl 3 the pellets were melted under pure argon in a high-frequency induction furnace on a water-cooled tantalum boat, turned upside-down and remelted three times. All four samples were not annealed. The alloys are hard, brittle and stable even in moist air and very likely congruently melting compounds. Optical microscopy showed the samples were nearly single phase with presence of a trace level of ThO 2 . For the arc melted ThCoGe and ThNiGe, an extra phase (1± 2%) contained in grain separation was observed and examined by electron microscopy equipped with a microanalysis system EDX. The analysis showed tern- ary phase with a composition Th 33 Co 27 Ge 40 for ThCoGe and ThNi 2 Ge 2 for ThNiGe sample. X-ray analysis was performed on powders in a Guinier-Stoe camera, using pure silicon as internal standard (a=5.4308 A Ê ). Both ThCoGe and ThNiGe were found to crystallise in the hexagonal AlB 2 -type structure. For ThCoGe a structure re®nement was carried out on sin- gle crystal. For this purpose, a small alloy was annealed by heating in an induction furnace for 2 h at about 0966-9795/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0966-9795(99)00047-3 Intermetallics 7 (1999) 1291±1294 * Corresponding author.