Classical Spin Nematic Transition in LiGa${}_{0.95}$In${}_{0.05}$Cr${}_4$O${}_8$

Abstract

We present the results of a combined ${}^7$Li NMR and diffraction study on LiGa${}_{0.95}$In${}_{0.05}$Cr${}_4$O${}_8$, a member of LiGa${}_{1-x}$In${}_x$Cr${}_4$O${}_8$ "breathing" pyrochlore family. Via specific heat and NMR measurements, we find that the complex sequence of first-order transitions observed for $x=0$ is replaced by a single, apparently second-order transition at $T_f=11$ K. Neutron and X-ray diffraction rule out both structural symmetry lowering and magnetic long-range order as the origin of this transition. Instead, reverse Monte Carlo fitting of the magnetic diffuse scattering indicates that the low temperature phase may be described as a collinear spin nematic state, characterized by a quadrupolar order parameter. This state also shows signs of short range order between collinear spin arrangements on tetrahedra, revealed by mapping the reverse Monte Carlo spin configurations onto a three-state color model describing the manifold of nematic states.

11 pages, 10 figures