The effect of uniaxial pressure on the antiferromagnetic structure of UNiAl studied using single-crystal neutron diffraction.

The effect of uniaxial pressure on the magnetic ordering in a single-crystalline sample of UNiAl has been studied by means of neutron diffraction. The crystal and magnetic structures remain in a first approximation unaffected for the pressure applied along the c axis. For perpendicularly applied pressure, severe changes to the magnetic ordering are found. From the original six magnetic reflections that are associated with each nuclear reflection, two disappear and the remaining four rotate in the reciprocal plane, marking modification of the propagation vector. The U magnetic moments are reduced upon application of the pressure along the a axis, by about 0.11 μ(B) kbar(-1). In contrast, the magnetic phase transition temperature increases by about 0.6 K kbar(-1). The results are explained qualitatively in terms of pressure-induced changes of exchange interactions.