Collinear spinwave calculations
Calculates linear spinwave theory Hamiltonians
This is the collinear only version of the work in J. Phys.: Condens. Matter 27 (2015) 166002.
For 2D materials only, this code can also calculate the magnetization vs. temperature curves.
If you use this code, please cite: https://arxiv.org/abs/2205.00300 and https://iopscience.iop.org/article/10.1088/0953-8984/27/16/166002/meta
Here is an example given for the ferromagnetic CrI3 using magnetic coupling parameters in 2D Mater. 4 (2017) 035002.
import matplotlib.pyplot as plt
sw = Spinw()
# POSCAR should be in the "directory as below"
# If OUTCAR is also in the same directory, magnetic moments are read from OUTCAR.
# If not, then each atomic magnetic moment must be supplied in "spins".
sw.read_structure(directory="./", spins=[3,3,0,0,0,0,0,0])
# define magnetic interactions
# This example uses 2D CrI3 structure.
# Reference values are taken from 2D Mater. 4 (2017) 035002:
# * isotropic exchange J is defined as 2.2 meV
# * anisotropic exchange lambda is defined as 0.09 meV
# Negative sign of J denotes that interactions are ferromagnetic.
# In XXZ hamiltonian, lambda is the anisotropic exchange in z-direction
# Hence it is the 3rd element of the np.diag([0,0,-0.09]) vector below.
# For lambda, the convention is to use negative sign for the favored
# anisotropy direction and use zero for the unfavorable directions.
# rmax = 4.5 A means only first nearest neighbors for this example
sw.add_coupling(('Cr1', 'Cr2'), -2.2, rmax=4.5)
sw.add_coupling(('Cr1', 'Cr2'), np.diag([0,0,-0.09]), rmax=4.5)
# plot magnon band structure
# compare to 2D Mater. 4 (2017) 035002
ax = plt.figure().gca()
sw.get_band_structure(ax, [0.0,0.0,0.0], [0.333333, 0.3333333, 0.0], num_k=100, normalize = True)
# normalize tag normalizes the energy axis in the band structure to JS units.
figname = './band_line.pdf'
plt.xlabel('k*l')
plt.savefig(figname, format='pdf')
# plot magnetization curve
sw.magnetization(kgrid=[20,20,1], tmin = 1, tmax = 100, dt = 1)CrI3 magnon dispersion curve:
CrI3 magnetization curve:
