Fragile antiferromagnetism in the heavy-fermion compound YbBiPt

We report results from neutron scattering experiments on single crystals of YbBiPt that demonstrate antiferromagnetic order characterized by a propagation vector, ${\mathit{\tau }}_{\mathrm{AFM}}$ = ($\frac{1}{2}\frac{1}{2}\frac{1}{2}$), and ordered moments that align along the [1 1 1] direction of the cubic unit cell. We describe the scattering in terms of a two-Gaussian peak fit, which consists of a narrower component that appears below $T_{\mathrm{N}}\approx 0.4$ K and corresponds to a magnetic correlation length of ${\xi }_{\mathrm{n}}\approx$ 80 $\AA$, and a broad component that persists up to $T^{*}\approx$ 0.7 K and corresponds to antiferromagnetic correlations extending over ${\xi }_{\mathrm{b}}\approx$ 20 $\AA$. Our results illustrate the fragile magnetic order present in YbBiPt and provide a path forward for microscopic investigations of the ground states and fluctuations associated with the purported quantum critical point in this heavy-fermion compound.

Figure 1

Contour plots of diffraction data taken for points in the ($HHL$) plane corresponding to the antiferromagnetic propagation vector ${\mathit{\tau }}_{\mathrm{AFM}}$ = ($\frac{1}{2}\frac{1}{2}\frac{1}{2}$). The intensity of the scattering is indicated by color. (a) Data for the ($\frac{1}{2}\frac{1}{2}\frac{5}{2}$) position for $T$ = 0.1 K and (b) $T$ = 0.75 K, and (c) after subtracting $T$ = 0.1 K data by the $T$ = 0.75 K data. Panels (d) and (e) show data for the ($\frac{1}{2}\frac{1}{2}\frac{3}{2}$) and ($\frac{1}{2}\frac{1}{2}\frac{1}{2}$) positions, respectively, after subtracting the $T$ = 0.1 K data by the corresponding $T$ = 0.8 K data. (f) Diagram of the ($HHL$) reciprocal lattice plane for YbBiPt. Nuclear Bragg points are indicated by black crosses, and possible magnetic Bragg points are indicated by circles. Solid circles correspond to measured points, and points where the intensity of the magnetic scattering is zero are marked with $\times$'s. Dashed lines indicate the magnetic Brillouin zones.

Figure 2

Detailed scattering data for ($\frac{1}{2}\frac{1}{2}\frac{3}{2}$). (a) Data from a rocking scan taken at $T$ = 0.08 K. Blue and red lines show the broad and narrower components of the two-Gaussian peak fit, respectively, and the shaded red area corresponds to scattering contributed by the narrower Gaussian peak. Black crosses at the bottom show scaled data from a rocking scan at the (1 1 1) nuclear Bragg peak, which is split due to a small misalignment of the two co-aligned crystals. (b) Data from rocking scans taken at $T$ = 0.45 K (open circles) and 0.75 K (filled dark gray circles). The blue curve represents a fit to a single Gaussian peak, while the dark gray line depicts the background. (c) $Q$ dependence of the scattering at ($\frac{1}{2}\frac{1}{2}\frac{3}{2}$) and ($\frac{1}{2}\frac{1}{2}\frac{5}{2}$) compared to the square of the Yb${}^{3+}$ magnetic form factor (solid line). (d) Energy dependence of the scattering from constant $\mathbf{Q}$ scans at $T$ = 0.08 K for Q = ($\frac{1}{2}\frac{1}{2}\frac{3}{2}$) (upward pointing triangles), and background scans at two different Q positions (circles and downward pointing triangles). Lines represent fits to Gaussian peaks, and the energy resolution (FWHM) is indicated by the horizontal line. Uncertainties represent one standard deviation.

Figure 3

Temperature dependence of the integrated intensities of the narrower (left axis) and broad (right axis) components of the two-Gaussian peak fits to the magnetic scattering at ($\frac{1}{2}\frac{1}{2}\frac{3}{2}$).