Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2003-09-08
Phys. Rev. B 68, 134451 (2003)
Physics
Condensed Matter
Strongly Correlated Electrons
13 pages, submitted to PRB
Scientific paper
10.1103/PhysRevB.68.134451
A modification of the ground state of the classical-spin Heisenberg Hamiltonian in the presence of a weak superstructural distortion of an otherwise Bravais lattice is examined. It is shown that a slight modulation of the crystal lattice with wavevector $\bQ_c$ results in a corresponding modulation of the exchange interaction which, in the leading order, is parametrized by no more than two constants per bond, and perturbs the spin Hamiltonian by adding the ``Umklapp'' terms $\sim S^\alpha_{\bq} S^\alpha_{\bq \pm \bQ_c}$. As a result, for a general spin-spiral ground state of the non-perturbed exchange Hamiltonian, an incommensurate shift of the propagation vector, $\bQ$, and additional new magnetic Bragg peaks, at $\bQ \pm n\bQ_c$, $n = 1,2,...$, appear, and its energy is lowered as it adapts to the exchange modulation. Consequently, the lattice distortion may open a region of stability of the incommensurate spiral phase which otherwise does not win the competition with the collinear N\'{e}el state. Such is the case for the frustrated square-lattice antiferromagnet. In addition, the ``Umklapp'' terms provide a commensuration mechanism, which may lock the spin structure to the lattice modulation vector $\bQ_c$, if there is sufficient easy-axis anisotropy, or a magnetic field in an easy plane.
No associations
LandOfFree
Heisenberg magnet with modulated exchange does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Heisenberg magnet with modulated exchange, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heisenberg magnet with modulated exchange will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-47566