Antiferromagnetic order in the quasicrystal approximant Cd${}_6$Tb studied by x-ray resonant magnetic scattering

We have used x-ray resonant magnetic scattering at the Tb $L_2$ edge to elucidate the nature of magnetic ordering in Cd${}_6$Tb, a 1/1 approximant closely related to the Cd-Mg-R (R = rare earth) icosahedral alloys. Below $T_N\approx 24$ K, the ordered moments associated with the icosahedral clusters at the corners and body center of the pseudocubic unit cell are antiferromagnetically correlated, and long-range magnetic order is realized.

Figure 1

Arrangement of Tb ions in the high-temperature cubic unit cell of Cd${}_6$Tb viewed along one of the cubic axes. The network of Tb ions can be viewed either as (a) a bcc packing of icosahedra or (b) a set of corner-sharing tilted octahedra.

Figure 2

Distribution of charge and magnetic peaks measured by an (a) H scan, (b) K scan, and (c) L scan through the (14 0 0) charge peak position and an (e) H scan, (f) K scan, and (g) L scan through the (15 0 0) magnetic peak position. Panels (d) and (h) plot the charge and magnetic peak positions schematically.

Figure 3

The fluorescence (open circles) and magnetic intensity (closed circles) measured around the (9 0 0) magnetic peak as a function of the incident beam energy through the Tb $L_2$ edge at $T=6$ K.

Figure 4

The temperature dependence of the magnetic peak intensity (open circles) measured without an analyzer and integrated intensity (filled circles) measured with polarization analysis at the (9 0 0) magnetic peak position referenced to the cubic unit cell. The inset shows the magnetic peak at $T=6$ K and its absence at 30 K (above $T_N$).