Magnetic anisotropy of single-crystalline

Abstract

We report the magnetic field dependence of the dc susceptibility and resistivity in superconducting single crystals of the hexagonal heavy-fermion superconductor UNi 2 Al 3. From the susceptibility we derive a crystalline-electric-field scheme, which closely resembles that of UPd 2 Al 3. 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 a-or c-axis T N is monotonically lowered, this is not the case for B b. Instead, here we find a field-induced magnetic transition into a, presumably, commensurate ordered magnetic state. We discuss our results on UNi 2 Al 3 in comparison to those for the related system UPd 2 Al 3 .

Magnetoresistance and Phase Diagram of Thin-Film UNi2Al3

“…Another difference between our thin film results and the previous single crystal measurements 8) becomes more obvious in Fig. 4, where we plot the magnetoresistance for differ- ent magnetic fields as a function of temperature.…”

“…The squares and the triangles correspond to the lower kink in the resistivity and the minimum in the derivative of the resistivity, respectively. The full and dashed black lines represent this phase boundary as determined by Süllow et al 8) and Tateiwa et al, 9) respectively. points for our measurements.…”

“…As observed previously, a plateau-like structure in the resistivity curve is the signature of T N in the a-axis resistivity. 8,15,21) With increasing applied magnetic field, this temperature range with reduced slope moves toward lower temperatures. Süllow et al took advantage of this effect to determine the phase boundary of the antiferromagnetic state in temperature-field-plane, 8) and we will follow this procedure here as well.…”

“…8,9) Given the important role of UPd 2 Al 3 for the understanding of unconventional superconductivity in heavy-fermions, 10,11) it is unfortunate that the experimental situation of UNi 2 Al 3 is still much less established than that of UPd 2 Al 3 . One reason for this is that the growth of single-crystalline samples of UNi 2 Al 3 is substantially more difficult than of UPd 2 Al 3 .…”

“…points for our measurements. For comparison, we also plot the phase boundary determined by Süllow et al 8) from resistivity and susceptibility measurements and by Tateiwa et al 9) from specific heat and magnetization measurements. In contrast to our thin-film experiments, those data were obtained on single crystals.…”