Spin-spin correlations in ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$: A polarized neutron scattering study

Polarized neutron diffraction and neutron spin echo have been employed to investigate the low-temperature magnetic correlations in the frustrated magnet . Several studies have reported a phase transition at , however, the low-temperature phase is still under debate. It has been reported that enters a frozen ferromagnetic phase, however, studies of the spin dynamics suggest otherwise. Our results conclusively rule out a frozen ferromagnetic state and confirm that the majority of the spin system continues to fluctuate below .

Figure 1

The two-metal-ion sublattice that runs through the oxide pyrochlores. In ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$, only the ${\mathrm{Yb}}^{3+}$ has a magnetic moment.

Figure 2

(Color online) The normalized intermediate scattering function from ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$. Squares and circles are above $\left(1\mathrm{K}\right)$ and below $\left(180\mathrm{mK}\right)$ the $0.24\mathrm{K}$ transition, respectively. Open symbols use the shortened setup (see text). The signal completely relaxes in the first $4\mathrm{ps}$. This is indicative of fast spin dynamics in a system, not unlike a paramagnet. The inset shows the $Q$ dependence of the magnetic scattering as determined from $xyz$ polarization analysis at $180\mathrm{mK}$.

Figure 3

Spin-flip (open circles) and non-spin-flip (closed circles) scattering at the (111) Bragg position. Above $240\mathrm{mK}$ there is only a small amount feed through due to incomplete polarization. At $90\mathrm{mK}$, a peak is clearly seen in the spin-flip data.