Source: LLB web
An easy-to-use and versatile software, SpinWave, to calculate spin waves in any arbitrary magnetic lattice, has been developed at the Laboratoire Léon Brillouin and is now freely available.
The calculation illustrated here has been performed for a right-handed crystal, using an Hamiltonian with 5 different exchanges, and an antisymmetric Dzyaloshinskii-Moriya (DM) term, whose vector is parallel to c. This DM term produces a gap in the lower branch of the dispersion and also selects the triangle magnetic chirality. The structural chirality is actually reflected in the S(Q,E) : the asymmetric spectral weight of the branches emerging from the - and + satellites is inverted for the other eniantomeric form (left-handed) of Ba3NbFe3Si2O14. For more details, see Parity Broken Chiral Spin Dynamics in Ba3NbFe3Si2O14, M. Loire, V. Simonet, S.Petit et al., Phys. Rev. Lett. 106, 207201 (2011).
Since the 1950’s, spin wave theory has been of fundamental importance in condensed matter physics. Spin waves are obtained from the linearization of the equation of motion, and can be seen as precession modes of the magnetically ordered structure, with typical energies of a few meV (or THz). Spin wave dispersions are routinely measured by neutron spectroscopy, and provide information about the coupling between spins and magnetic anisotropy parameters.
The spin wave calculating code, SpinWave, developed at the Laboratoire Léon Brillouin (LLB), allows one to simulate the spin waves spectra of commensurate, as well as incommensurate magnetic structures, using linear spin-wave theory. Magnetic interactions like Heisenberg, anisotropic, Dzyaloshinskii-Moriya, etc… can be included in the Hamiltonian. In addition to the dispersion, spin-spin correlation functions, chiral correlations, with or without magnetic form factor, can be calculated. Calculations in any direction of the reciprocal space, and constant energy cut calculations in any plane of the reciprocal space are possible, as well as the calculation of the powder-averaged spin wave spectrum. SpinWave also features the possibility to use classical energy minimization to determine the ground state magnetic structure (single k) for a set of magnetic exchange and anisotropies.
SpinWave is developed and maintained by Dr. Sylvain Petit at LLB. It can be downloaded at the following address: http://www-llb.cea.fr/logicielsllb/SpinWave/SW.html
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