Thermal-expansion and magnetostriction study on UNiAl single crystals

Abstract

We report on c-axis thermal-expansion and magnetostriction measurements on the antiferromagnet UNiAl TN=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 in zero magnetic field exhibits a minimum centered around 35 K≈2 TN, which is nearly removed in a field of 13 T. At low temperatures UNiAl undergoes a metamagnetic transition. The transition is sharp for T≤7 K and shows up at 11.4 T together with an abrupt magnetostriction change by ≈−1.7×10−4. 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>TN. These results suggest us to attribute the zero-field thermal expansion anomaly to antiferromagnetic correlations that survive in UNiAl at temperatures far above TN.