SpinW is a Matlab library that can plot and numerically simulate magnetic structures and excitations of given spin Hamiltonian using classical Monte Carlo simulation and linear spin wave theory.


Features:

In short SpinW can solve the following spin Hamiltonian using classical and quasi classical numerical methods:


\mathcal{H}=\sum_{i,j}\mathbf{S}_iJ_{ij}\mathbf{S}_j + \sum_i \mathbf{S}_iA_i\mathbf{S}_i + \mathbf{B}\sum_i\mathbf{g}_i\mathbf{S}_i

where S_i are spin vector operators, J_{ij} are 3x3 matrices describing pair coupling between spins, A_{ij} are 3x3 anisotropy matrices, B is external magnetic field and g_i is the g-tensor.

Crystal structures

  • definition of crystal lattice with arbitrary unit cell, using space group or symmetry operators
  • definition of non-magnetic atoms and magnetic atoms with arbitrary moment size
  • publication quality plotting of crystal structures (atoms, labels, axes, surrounding polyhedron, anisotropy ellipsoids, DM vector, etc.)

Magnetic structures

  • definition of 1D, 2D and 3D magnetic structures
  • representation of incommensurate structures using rotating coordinate system or complex basis vectors
  • generation of magnetic structures on a magnetic supercell
  • plotting of magnetic structures

Magnetic interactions

  • simple assignment of magnetic interactions to neighbouring magnetic atoms based on distance
  • possible interactions: Heisenberg, Dzyaloshinskii-Moriya, anisotropic and general 3x3 exchange tensor
  • arbitrary single ion anisotropy tensor (easy-plane, easy-axis, etc.)
  • Zeeman energy in homogeneous magnetic field including arbitrary g-tensor
  • calculation of symmetry allowed elements of the above tensors based on the crystallographic space group

Simulation of magnetic structures

  • classical energy minimization assuming single-k magnetic structure for fast and simple solution for ground state magnetic structure
  • simulated annealing using the Metropolis algorithm on an arbitrary large magnetic supercell
  • calculating properties in thermodynamical equilibrium (heat capacity, magnetic susceptibility, etc.)
  • magnetic structure factor calculation using FFT
  • simulation of magnetic neutron diffraction and diffuse scattering
  • Simulation of magnetic excitations in general commensurate and incommensurate magnetic structures using linear spin-wave theory
  • calculation of spin wave dispersion, spin-spin correlation functions
  • calculation of neutron scattering cross section for unpolarized neutrons including the magnetic form factor
  • calculation of polarized neutron scattering cross sections
  • possible to include different moment sizes for different magnetic atoms
  • calculation of powder averaged spin wave spectrum

Plotting of spin wave spectrum

  • plotting of dispersions and correlation functions
  • calculation and plotting of the convoluted spectra for direct comparison with inelastic neutron scattering
  • full integration into Horace for plotting and comparison with time of flight neutron data, see http://horace.isis.rl.ac.uk

Fitting spin wave spectra

  • possible to fit any parameter in the Hamiltonian
  • robust fitting, even when the number of simulated spin wave modes differs from the measured number of modes
Feel free to ask questions & requests!

Helmholtz-Zentrum BerlinNiels Bohr International AcademyISIS, Science   Technology Facilities Council