Structural and magnetic instabilities of layered magnetic systems

Abstract

We present a study of the magnetic order and the structural stability of two-dimensional quantum spin systems in the presence of spin-lattice coupling. For a square lattice it is shown that the plaquette formation is the most favourable form of static two-dimensional dimerization. We also demonstrate that such distortions may coexist with long range magnetic order, in contrast to the one-dimensional case. Similarly, the coupling to Einstein phonons is found to reduce, but not to eliminate the staggered magnetic moment. In addition, we consider the renormalization of the square lattice phonon spectrum due to spin-phonon coupling in the adiabatic approximation. Towards low temperatures significant softening mainly of zone boundary phonons is found, especially around the $(\pi ,0)$ point of the Brillouin zone. This result is compatible with the tendency to plaquette formation in the static limit. We also point out the importance of a "magnetic pressure" on the lattice due to spin-phonon coupling. At low temperatures, this results in a tendency towards shear instabilities of the lattice.

References in corpus (5)

• Spin-Phonon Chains with Bond Coupling
• Ground-state properties of two-dimensional dimerized Heisenberg models
• Quantum disorder due to singlet formation: The Plaquette lattice
• On the evaluation of the specific heat and general off-diagonal n-point correlation functions within the loop algorithm
• Thermodynamic properties of the two-dimensional S=1/2 Heisenberg antiferromagnet coupled to bond phonons

Cited by in corpus (4)

• Valence-Bond Order in a Honeycomb Antiferromagnet Coupled to Quantum Phonons
• Topological solitons and bulk polarization switch in collinear type II multiferroics
• Deconfinement phase transition in a two-dimensional model of interacting $2\times 2$ plaquettes
• Structural transition, spontaneous formation of strong singlet dimers and metamagnetism in $S=3/2$ magnetoelastic spin chains