Evidence for unidimensional low-energy excitations as the origin of persistent spin dynamics in geometrically frustrated magnets

Abstract

We report specific heat, magnetic, and muon spin relaxation measurements performed on a polycrystalline sample of the normal spinel ${\mathrm{CdHo}}_{2}{\mathrm{S}}_{4}$. The rare-earth ions sit on a lattice of corner-sharing regular tetrahedra as in pyrochlore compounds. Magnetic ordering is detected at ${T}_{\mathrm{c}}\ensuremath{\simeq}0.87$ K. From spin-lattice relaxation rate measurements on both sides of ${T}_{\mathrm{c}}$ we uncover similar magnetic excitation modes driving the so-called persistent spin dynamics at $T<{T}_{\mathrm{c}}$. Unidimensional excitations are argued to be at its origin. Often observed spin loop structures are suggested to support these excitations. The possibility of a generic mechanism for their existence is discussed.