PHYSICAL REVIEW B VOLUME 45, NUMBER 9 1 MARCH 1992-I Superconductivity in TaSi~ single crystals U. Gottlieb Laboratoire des Materiaux et du Genie Physique, Ecole Nationale Superieure de Physique de Grenoble, Institut National Polytechnique de Grenoble, Bohse Postale 46, 38402 St. Martin d'Heres, France and Centre de Recherches sur les Tres Basses Temperatures, Centre National de la Recherche Scientifique, BoAe Postale 166, 38042 Grenoble CEDEX 9, France J. C. Lasjaunias and J. L. Tholence Centre de Recherches sur les Tr'es Basses Temperatures, Centre National de la Recherche Scientigque, Boite Postale 166, 38042 Grenoble CEDEX 9, France O. Laborde Centre de Recherches sur les Tr'es Basses Temperatures, Centre National de la Recherche Scientigque, Borte Postale 166, 38042 Grenoble CEDEX 9, France and Seruice National des Champs Intenses, Centre National de la Recherche Scientigque, Boite Postale 166, 38042 Grenoble CEDEX 9, France O. Thomas and R. Madar Laboratoire des Materiaux et du Genie Physique, Ecole National Superieure de Physique de Grenoble, Institut National Polytechnique de Grenoble, Bowie Postale 46, 38402 St. Martin d'IIeres, France (Received 25 October 1991) We have measured the magnetization and the specific heat of single-crystalline TaSiz at very low tem- peratures (0. 1 K~ T 7. 5 K). TaSiz is superconducting below T, =0.353 K, with H, (T=O K) =2. 98 mT. We estimate and discuss the microscopic superconductivity parameters. TaSi& is found to be a type-I superconductor with weak electron-phonon coupling. Among the silicides of transition metals, some of the 215 compounds, like V3Si and Nb3Si, ' are known to be superconductors with high transition temperatures (T, =17. 1 K for V3Si). For the transition metal disili- cides, however, superconductivity has only been reported for one compound, CoSiz, with a critical temperature near 1 K. Superconductivity has already been found in thin films of TaSiz and NbSiz, but has not been confirmed on bulk samples. In order to continue our pre- vious investigations on the intrinsic characteristics and properties of the disilicides of transition metals, we have measured the magnetization and the low temperature specific heat of TaSiz single crystals. TaSiz crystallizes in the hexagonal C40 structure (space group P6z22}. Large single crystals of TaSiz were grown by a modified Czo- chralski technique. These crystals were of large size (several cm }, and of very good quality, which is reflected by the high residual resistance ratios (RRR)400, see Refs. 4, 6, and 7). The largest crystal was used for specific heat measurements. Smaller samples for resistivi- ty and magnetization measurements were cut from anoth- er crystal. Magnetization measurements were made by the extrac- tion (between two pick-up coils) technique; the field is given 'by a copper coil cooled by liquid nitrogen, and it can vary between — 300 mT and +300 mT with small hysteresis. The low temperatures were obtained with a miniaturized dilution refrigerator, which is moved with the sample. The sample was a single crystalline paral- lelepiped (=8X0. 6X0. 5 mm ) with length along the [1010] direction, mounted parallel to the field. In Fig. 1 we present the magnetization for two temperatures versus the effective magnetic field H, z at the sample sur- face. We obtained H, tt by correcting the applied field with the demagnetization factor N. N =1. 03 X 10 had been determined from the sample shape and it corre- ~ 5 7 I I I I I I I I I I 1 I I I I I I I I I I I I I f I I I I f I I I I I I I 0 0 lt i~%'gT $$+ggpl ~ I I I I I I I -0. 5 0 - 1 -1. 5 Tasi 2 2 I I I I I I I I I I I I 0 0.5 I l I I I I I I I I 1 I I i s i i I I I I I I I I 15 2 25 3 35 p, H(mT) FIG. 1. Magnetization vs effective magnetic field for 0.1 K (O: increasing field; ~: decreasing field) and 0. 25 K (0: in- creasing field; ~: decreasing field); plotted lines are a guide for the eye. 45 4803 1992 The American Physical Society