STRUCTURE AND MAGNETIC-PROPERTIES OF THE UNI10-XFEXSI2 SYSTEM AND SI-29 NUCLEAR-MAGNETIC-RESONANCE IN UNI10SI2

Structure and magnetic properties of UNi10-xFexSi2 intermetallics and Si-29 nuclear magnetic resonance (NMR) in UNi10Si2 are investigated in a wide temperature range. Solid solutions in the exactly single-phase tetragonal form, ThMn12 type, exist for x<2. The Ni and Fe atoms occupy the 8(f), 8(i) and 8(j) positions statistically, whereas the U atoms occupy the 2(a) and the Si atoms the 8(j) sites. The lattice parameters roughly follow Vegard's law. The magnetic susceptibility does not exhibit Curie-Weiss bebaviour and, at about 630 K, an anomaly in the temperature dependence is observed. At low temperature, other anomalies are observed at 32 K and 45 K, for x=0.5 and 1.0 respectively. These low temperature anomalies are probably connected with magnetic ordering of a ferromagnetic character, whereas that at 630 K might result from the superparamagnetic state of Ni. Two Si-29 NMR lines in UNi10Si2 were observed with the Knight shift being temperature independent in the 4.2-294 K range. The spin-lattice relaxation rates are measured in the 4.2-30 K temperature range and they are roughly proportional to the temperature.