Magnetic anisotropy of single-crystalline UNi2Al3

We report the magnetic field dependence of the de susceptibility and resistivity in superconducting single crystals of the hexagonal heavy-fermion superconductor UNi2Al3. From the susceptibility we derive a crystalline-electric-field scheme, which closely resembles that of UPd2Al3. Furthermore, we examine the magnetic phase transition into the incommensurably ordered state at T-N = 4.1 K and construct the magnetic phase diagram for the three crystallographic directions. While for fields B parallel to the alpha- or c-axis T-N is monotonically lowered, this is not the case for B parallel to b. Instead. here we find a field-induced magnetic transition into a, presumably, commensurate ordered magnetic state. We discuss our results on UNi2Al3 in comparison to those for the related system UPd2Al3.