Linewidths of spin waves in magnetic film

In this example, we show how to calculate the line widths of the Damon-Eshbach modes in a 50 nm thick permalloy film. Since the line widths are calculated from the mode profiles, first, we calculate the linear spectrum.

import tetrax as tx
import numpy as np

Dispersion calculation

For the numerical calculations with TetraX, we create a permalloy film with 50 nm thickness and a line trace mesh along the thickness with 1 nm resolution. Remember: the normal direction is the \(y\) direction, and the propagation direction is the \(z\) direction. We also set permalloy material paremeters.

T = 50
sample = tx.Sample(tx.geometries.layer.monolayer(thickness=T,cell_size=1))
sample.material = tx.materials.permalloy

The film is magnetized along the \(x\) direction, using an external magnetic field of 20 mT, thus the wave vector is perpendicular to the equilibrium magnetization.

sample.mag = (1,0,0)


Bext = 20e-3
sample.external_field = (Bext,0,0)

The linewidths will be calculated from the mode profiles (more specifically, from the mode ellipticities) of a calculated eigenspectrum, see Ref. 2 or Ref. 3. By default, the mode profiles will always be saved. Nevertheless, if you set save_mode_profiles=False, line widths CANNOT can be calculated.

spectrum_DE = tx.experiments.eigenmodes(sample, num_modes=3,num_cpus=-1, num_k=201, save_mode_profiles=True)

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We can visualize the calculated dispersion easily using the built-in plot() methdod of the EigenResult.

spectrum_DE.plot(n=[0,2], k=(0,40e6), fscale="G", kscale="u", renderer="notebook") # remove the renderer argument when running on your computer)

Linewidths

Now, we can calculate the line widths. Calling plot_linewidths() method of the EigenResult spectrum_DE will automatically calculate them from the mode profiles. The avoided level crossing between the first and the second mode is also seen in the line widths.

spectrum_DE.plot_linewidths(n=[0,2], k=(0,40e6), fscale="M", kscale="u",renderer="notebook") # remove the renderer argument when running on your computer)