Mesoscopic correlations in Tb2Ti2O7 spin liquid

TL;DR

This study reveals mesoscopic spin correlations with a specific propagation vector in Tb2Ti2O7 spin liquid at very low temperatures, showing both spin-ice-like and monopole-like structures, with implications for understanding its magnetic order.

Contribution

It provides the first detailed analysis of mesoscopic correlations and possible spin structures in Tb2Ti2O7, combining neutron diffraction and specific heat data to identify spin textures.

Findings

Mesoscopic correlations involve Tb moments of 1-2 μB on ~20 Å scale.

Long-range order with small moments detected in some samples.

Two possible spin structures: spin-ice-like and monopole-like correlations.

Abstract

We have studied the spin correlations with $\bf{k}$= ($\frac12$, $\frac12$, $\frac12$) propagation vector which appear below 0.4\, K in \tbti\ spin liquid by combining powder neutron diffraction and specific heat on Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$ samples with $x$=0, 0.01, -0.01. The $\bf{k}$= ($\frac12$, $\frac12$, $\frac12$) order clearly appears on all neutron patterns by subtracting a pattern at 1.2(1)\,K. Refining the subtracted patterns at 0.07\,K yields two possible spin structures, with spin-ice-like and monopole-like correlations respectively. Mesoscopic correlations involve Tb moments of 1 to 2 \mub\ ordered on a length scale of about 20 \AA. In addition, long range order involving a small spin component of 0.1 to 0.2 \mub\ is detected for the $x$= 0 and 0.01 samples showing a peak in the specific heat. Comparison with previous single crystals data suggests that the ($\frac12$, $\frac12$, $\frac12$) order settles in through nanometric spin textures with dominant spin ice character and correlated orientations, analogous to nanomagnetic twins.