Frustrated Heisenberg J1-J2 model within the stretched diamond lattice of LiYbO2

We investigate the magnetic properties of LiYbO2, containing a three-dimensionally frustrated, diamondlike lattice via neutron scattering, magnetization, and heat capacity measurements. The stretched diamond network of Yb3+ ions in LiYbO2 enters a long-range incommensurate, helical state with an ordering wave vector k = (0.384,+/- 0.384, 0) that "locks-in" to a commensurate k = (1/3,+/- 1/3, 0) phase under the application of a magnetic field. The spiral magnetic ground state of LiYbO2 can be understood in the framework of a Heisenberg J(1)-J(2) Hamiltonian on a stretched diamond lattice, where the propagation vector of the spiral is uniquely determined by the ratio of J(2)/vertical bar J(1 vertical bar). The pure Heisenberg model, however, fails to account for the relative phasing between the Yb moments on the two sites of the bipartite lattice, and this detail as well as the presence of an intermediate, partially disordered, magnetic state below 1 K suggests interactions beyond the classical Heisenberg description of this material.