Quantum spin configurations in Tb2Ti2O7

Low energy collective angular momentum states of the Tb3+ ions in Tb2Ti2O7 are classified according to the irreducible representations of the octahedral point group. Degeneracy lifting due to the exchange interaction is discussed. Diffuse neutron scattering intensity patterns are calculated for each collective angular momentum state and the ground state is inferred by comparing to experiment.Comment: 5 pages, 1 colour figure. Slight corrections and additions to text and figur

Structural distortion and the spin liquid state in Tb2Ti2O7

It is shown that a k=0, A_{2u} distortion of the terbium tetrahedral network in Tb2Ti2O7 accounts for the apparent isolation of single tetrahedra as seen in neutron scattering studies. Single tetrahedron collective spin states, rather than individual spins, account for the main features of the spin liquid state, namely, fluctuating local moments and the absence of long range order. Singlet and doublet collective spin ground states are considered. An effective interaction between tetrahedra on the fcc lattice is derived and found to be weak and anisotropic.Comment: 5 page

Exact diagonalization for spin-1/2 spin ice pyrochlores

We find exact solutions to the Hamiltonian of a 16-site spin-1/2 pyrochlore crystal with nearest neighbour exchange interactions. The methods of group theory (symmetry) are used to completely block-diagonalize the Hamiltonian, yielding precise details about symmetry of the eigenstates, in particular those components which are {\em spin ice} states, in order to evaluate the spin ice density at finite temperature. At low enough temperatures, a `perturbed' spin ice phase is clearly outlined within the four parameter space of the general model of exchange interactions. The quantum spin ice phase is expected to exist outside these boundaries

Symmetry considerations in exact diagonalization: spin-1/2 pyrochlore magnets

We describe how the methods of group theory (symmetry) are used to optimize the problem of exact diagonalization of a quantum system on a 16-site pyrochlore lattice. By analytically constructing a complete set of symmetrized states, we completely block-diagonalize the Hamiltonian. As an example, we consider a spin-1/2 system with nearest neighbour exchange interactions

Theory of magnetic phases of hexagonal rare earth manganites

The magnetic phases of hexagonal perovskites RMnO_3 (R=Ho, Er, Tm, Yb, Sc, Y) are analysed using group theory and the Landau theory of phase transitions. The competition between various magnetic order parameters is discussed in the context of antiferromagnetic interactions. A phenomenological model based on four one-dimensional magnetic order parameters is developed and studied numerically. It is shown that coupling of the various order parameters leads to a complex magnetic field-temperature phase diagram and the results are compared to experiment.Comment: 11 pages, 14 figures. Manuscript with higher quality figures can be obtained here: http://www.physics.mun.ca/~curnoe/papers/RMnO3.submit.pd

Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12

Electronic state evolution in the metal-non-metal transition of PrRu4P12 has been studied by X-ray and polarized neutron diffraction experiments. It has been revealed that, in the low-temperature non-metallic phase, two inequivalent crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2) ground states are located at Pr1 and Pr2 sites forming the bcc unit cell surrounded by the smaller and larger cubic Ru-ion sublattices, respectively. This modulated electronic state can be explained by the p-f hybridization mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f hybridization effect plays an important role for the electronic energy gain in the metal-non-metal transition originated from the Fermi surface nesting.Comment: 5 pages, 5 figures. Accepted by J. Phys. Soc. Jp