https://doi.org/10.1007/s100510170052
Magnetic properties and spin waves of bilayer magnets in a uniform field
1
Institut für Theoretische Physik, Technische Universität Dresden, 01062 Dresden, Germany
2
Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut für Physik, Universität Augsburg,
86135 Augsburg, Germany
Corresponding author: a matthias.vojta@physik.uni-augsburg.de
Received:
23
April
2001
Published online: 15 October 2001
The two-layer square lattice quantum antiferromagnet with spins 
shows a
zero-field magnetic order-disorder transition at a critical ratio of the inter-plane to
intra-plane couplings.
Adding a uniform magnetic field tunes the system to canted antiferromagnetism and
eventually to a fully polarized state;
similar behavior occurs for ferromagnetic intra-plane coupling.
Based on a bond operator spin representation, we propose an approximate ground state
wavefunction which consistently covers all phases by means of a
unitary transformation.
The excitations can be efficiently described as independent bosons;
in the antiferromagnetic phase these reduce to the well-known spin waves, whereas
they describe gapped spin-1 excitations in the singlet phase.
We compute the spectra of these excitations as well as the
magnetizations throughout the whole phase diagram.
PACS: 73.43.Nq – Quantum phase transitions / 75.10.Jm – Quantized spin models / 75.50.Ee – Antiferromagnetics
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001
