Magnetic order in GdBiPt studied by x-ray resonant magnetic scattering

Rare-earth ($R$) half-Heusler compounds $R$BiPt exhibit a wide spectrum of interesting ground states. We have employed x-ray resonant magnetic scattering to elucidate the microscopic details of the magnetic structure in GdBiPt below $T_N=8.5$ K. Experiments at the Gd $L_2$ absorption edge show that the Gd moments order in an antiferromagnetic stacking along the cubic diagonal $\left[111\right]$ direction, satisfying one of the requirements for an antiferromagnetic topological insulator as proposed previously, where both time-reversal symmetry and lattice translational symmetry are broken, but their product is conserved.

Figure 1

Crystal structure of GdBiPt.

Figure 2

Resonant magnetic scattering from the GdBiPt single crystal. (a) Rocking scans ($\theta$) through the $(\frac{1}{2}-\frac{1}{2}\frac{13}{2})$ magnetic peak position above (open circles) and below (solid circles) $T_N$ taken in $\sigma$-$\pi$ scattering geometry using the PG $\left(006\right)$ analyzer. (b) Energy scan through the Gd $L_2$ absorption edge at the $(\frac{1}{2}-\frac{1}{2}\frac{13}{2})$ magnetic peak position at $T=4.7$ K (blue/gray solid circles) along with the measured x-ray fluorescence from the sample (black solid circles).

Figure 3

(a) $M/H$ and its temperature derivative for GdBiPt. (b) The magnetic intensity measured while scanning temperature at the maximum of the $\left(\frac{1}{2}\frac{1}{2}\frac{9}{2}\right)$ diffraction peak without a polarization analyzer (open small circles) and the integrated intensity of the $(\frac{1}{2}-\frac{1}{2}\frac{13}{2})$ diffraction peak measured at selected temperatures using the polarization analyzer (open large squares). The solid line is a power-law fit to the integrated intensity data as described in the text.

Figure 4

Integrated intensity in azimuth scans through the $(-\frac{1}{2}-\frac{1}{2}\frac{13}{2})$ magnetic Bragg peak. Measured data are depicted by solid black circles. Solid and dashed lines represent calculations for selected magnetic moment directions in a single magnetic domain, and for intensity from equally populated domains averaged over the three possible symmetry-equivalent magnetic moment orientations, respectively.