157 research outputs found
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
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
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
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