Magnetic ordering and spin excitations in the frustrated magnetMnSc2S4

The $A$-site spinel compound $\mathrm{Mn}{\mathrm{Sc}}_2{\mathrm{S}}_4$ exhibits strong frustration effects with a low ordering temperature $(T_N=2.3\mathrm{K})$. Detailed neutron-scattering investigations have been performed to study the magnetic ordering process and the associated magnetic excitations. The magnetic structure found at $T=1.5\mathrm{K}$ is a spiral within the $a\text{−}b$ plane characterized by a propagation vector of $\mathbf{q}=(3∕4,3∕4,0)$. The magnetic ordering process is spectroscopically reflected by a change from a purely quasielastic to an inelastic response. The quasielastic line width corresponds to a magnetic energy scale of $\approx 1\mathrm{meV}$ which is consistent with the spin wave stiffness as determined from the magnon dispersion at low temperatures.