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REAL MAGNETIC MATERIALS exhibit a macroscopic quantum state
in which the atomic moments interact through quantum-mechanical
'exchange forces'. These result from overlap of atomic wave functions and can
favour parallel (ferromagnetic) or antiparallel (antiferromagnetic) alignment
of moments. The low energy states then minimise the sum of all
pair interactions, and, because of geometrical constraints, not all pairs
can
adopt their lowest energy state. This is termed frustration, and can lead
to complex magnetic structures as well as complete breakdown of magnetic order.
During 1999 we have continued a program of study of such systems,
based on both analytic and numerical techniques. Some of the
completed work includes: |
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a study of the low energy excited states of the
J1-J2 model (square lattice with first and second
interactions) in the quantum disordered
"spin-liquid" phase
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strong evidence that the ground state in the same region has dimer order
with striped correlations. This may be related to the striped phases
observed experimentally in the cuprate superconductors
- the first detailed theoretical study of the magnetic structure and
phase diagram of the quasi-two-dimensional material SrCu2(BO3)2, found by a Japanese group in 1999.
Valeri Kotov, Jaan
Oitmaa,
Oleg Sushkov & Wei Hong Zheng
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