Thermal expansion of single-crystalline UNiAl

Abstract

Magnetization, magnetic susceptibility, electrical resistivity, and specific heat measurements of UNiAl point to antiferromagnetic ordering below 19.3 K, which is confirmed by neutron-diffraction experiments. The enhanced γ value of 167 mJ/mol K2 is reflecting pronounced presence of magnetic fluctuations, which influence also the other electronic properties down to low temperatures. The thermal expansion of UNiAl was measured in the temperature range 1.5–210 K on a single crystal along the a and c axis. Similar to other bulk properties, also the thermal expansion of UNiAl is highly anisotropic. The a axis is monotonously expanding with increasing temperature in the whole temperature range. Along the c axis, the lattice first collapses with increasing temperature up to 35 K. Around this temperature, the thermal expansion coefficient αc changes sign and continuous expansion with further increasing temperature is then observed. The sharp anomaly of α near 19.3 K present in both directions is consistent with the magnetic phase transition. The results are discussed in terms of the presence of anisotropic magnetic fluctuations.