Magnetic properties and spin waves of bilayer magnets in a uniform field |
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| Authors: | T. Sommer M. Vojta K.W. Becker |
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| Affiliation: | Institut für Theoretische Physik, Technische Universit?t Dresden, 01062 Dresden, Germany, DE
Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut für Physik, Universit?t Augsburg, 86135 Augsburg, Germany, DE
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| Abstract: | The two-layer square lattice quantum antiferromagnet with spins 12 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. Received 23 April 2001 |
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| Keywords: | PACS. 73.43.Nq Quantum phase transitions – 75.10.Jm Quantized spin models – 75.50.Ee Antiferromagnetics |
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