Square-lattice Heisenberg antiferromagnet with two kinds of nearest-neighbor regular bonds
- Institute for Solid State Physics, Bulgarian Academy of Sciences, Tzarigradsko chaussee-72, 1784 Sofia (Bulgaria)
- Institut fuer Theoretische Physik, Universitaet Magdeburg, P.O. Box 4120, D-39016 Magdeburg (Germany)
We study the zero-temperature phase diagram of a square-lattice {ital S}=1/2 Heisenberg antiferromagnet with two types of regularly distributed nearest-neighbor exchange constants, {ital J}{sub 1}{approx_gt}0 (antiferromagnetic) and {minus}{infinity}{lt}{ital J}{sub 2}{lt}{infinity}, using spin-wave series based on appropriate mean-field Hamiltonian and exact-diagonalization data for small clusters. At a semiclassical level, the model displays two critical points separating the N{acute e}el state from (i) a helicoidal magnetic phase for relatively small frustrating ferromagnetic couplings {ital J}{sub 2}{lt}0 ({ital J}{sub 2}/{ital J}{sub 1}{lt}{minus}1/3 for classical spins), and (ii) a finite-gap quantum paramagnetic phase for large enough antiferromagnetic exchange constants {ital J}{sub 2}{approx_gt}0. The quantum order-disorder transition (ii) is similar to the one recently studied in two-layer Heisenberg antiferromagnets and is a pure result of the zero-point spin fluctuations. On the other hand, the melting of the N{acute e}el state in the ferromagnetic region, {ital J}{sub 2}{lt}0, is a combined effect of the frustration and quantum spin fluctuations. The second-order spin-wave calculations of the ground-state energy and on-site magnetization are in accord with our exact-diagonalization data in a range away from the quantum paramagnetic phase. In approaching the phase boundary, the theory fails due to the enhanced longitudinal-spin fluctuations, as it has recently been argued by Chubukov and Morr.
- OSTI ID:
- 278705
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 53, Issue 5; Other Information: PBD: Feb 1996
- Country of Publication:
- United States
- Language:
- English
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