Rods of Neutron Scattering Intensity in ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$: Compelling Evidence for Significant Anisotropic Exchange in a Magnetic Pyrochlore Oxide

Paramagnetic correlations in the magnetic material ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ have been investigated via neutron scattering, revealing a [111] rod of scattering intensity. Assuming interactions between the ${\mathrm{Yb}}^{3+}$ ions composed of all symmetry-allowed nearest neighbor exchange interactions and long-range dipolar interactions, we construct a model Hamiltonian that allows for an excellent description of the neutron scattering data. Our results provide compelling evidence for significant anisotropic exchange interactions in an insulating magnetic pyrochlore oxide. We also compute the real space correlations leading to the [111] rod of scattering.

Figure 1

Neutron scattering (NS) maps in the ($h$, $k$, $k$) plane. (a) and (b) show experimental data at 9.1 and 1.4 K, respectively. In (b), a rod of scattering intensity along [111] is clearly seen, while in (a) the rod is not strong. (c) shows a comparison between experimental data and the computed NS intensity at 1.4 K along [$3-k$, $k$, $k$] for both isotropic exchange and the full model. (d) shows computed NS using the Hamiltonian $H$ (see text), at $T=1.4\mathrm{K}$. (e) shows the calculated NS using $H$ with only isotropic exchange determined from fitting ${\theta }_{\mathrm{CW}}$ and long-range dipolar interactions at $T=1.4\mathrm{K}$. (f) shows experimental neutron scattering at 1.4 and 9.1 K along the line [$h$, 2.25, 2.25] showing that the feature between $h=3$ and $h=4$ does not change in intensity with temperature. The white arrows in (a) and (b) indicate the range $h\in [3,4]$ in [$h$, 2.25, 2.25] in (f).

Figure 2

Real space spin-spin correlation functions (a) $S(\mathbf{r})$ and (b) $S_{\perp }(\mathbf{r})$ (see text) computed at $T=1.4\mathrm{K}$ using the anisotropic exchange model and plotted along various crystallographic directions.