Direct measurement of the spin gap in a quasi-one-dimensional clinopyroxene: NaTiSi2O6

True inorganic spin-Peierls materials are extremely rare, but NaTiSi2O6 was at one time considered to be an ideal candidate owing to its well separated chains of edge-sharing TiO6 octahedra. At low temperatures, this material undergoes a phase transition from C2/c to P1¯ symmetry, where Ti3+-Ti3+ dimers begin to form within the chains. However, it was quickly realized with magnetic susceptibility that simple spin fluctuations do not progress to …