One-dimensional quantum magnetism in the anhydrous alum KTi(SO4)(2)
The anhydrous alum KTi(SO4)(2), where the Ti3+ (d(1), S = 1/2) ions form an anisotropic triangular lattice, has been prepared by a new hydrothermal route and characterized by magnetic susceptibility and neutron scattering measurements. Contrary to expectations, fits to the magnetic susceptibility indicate that the spins are isotropic (i.e. Heisenberg) and that the frustrating couplings are weak; indeed, the system is well modelled by nearly isolated chains. The inelastic neutron scattering data furthermore shows excellent agreement with an exact theoretical calculation for the one-dimensional spinon continuum. The unexpected magnetic properties of KTi(SO4)(2) are explained in the light of density functional calculations, which reveal an unusual orbital ground state for the Ti3+ ion.