Thermal-expansion and magnetostriction study on UNiAl single crystals

We report on c-axis thermal-expansion and magnetorestriction measurements on tire antiferromagnet UNiAl T-N = 19.3 K) in the temperature range of 2 - 90 K and in magnetic fields up to 13 T applied along c. The thermal expansion of UNiAl hi zero magnetic field exhibits a minimum centered around 35 K approximate to 2 T-N, which is nearly removed in a field of 13 T. At low temperatures UNiAl undergoes a metamagnetic transition. The transition is sharp for T less than or equal to 7 K and shows up at 11.4 T together with arc abrupt magnetostriction change by approximate to - 1.7x10(-4). For T increasing above 7 K, the metamagnetic transition related magnetostriction feature becomes gradually smeared out but a negative magnetostriction is observed even for T > T-N. These results suggest us to attribute the zero-field thermal expansion anomaly to antiferromagnetic correlations that survive in UNiAl at temperatures far above T-N.